diff --git a/crates/backend/src/ast.rs b/crates/backend/src/ast.rs
index 2b4dfa93..3262caf9 100644
--- a/crates/backend/src/ast.rs
+++ b/crates/backend/src/ast.rs
@@ -7,7 +7,8 @@ pub struct NapiFn {
   pub js_name: String,
   pub attrs: Vec<Attribute>,
   pub args: Vec<NapiFnArgKind>,
-  pub ret: Option<(syn::Type, /* is_result */ bool)>,
+  pub ret: Option<syn::Type>,
+  pub is_ret_result: bool,
   pub is_async: bool,
   pub fn_self: Option<FnSelf>,
   pub kind: FnKind,
diff --git a/crates/backend/src/codegen/fn.rs b/crates/backend/src/codegen/fn.rs
index e44666a0..0a009516 100644
--- a/crates/backend/src/codegen/fn.rs
+++ b/crates/backend/src/codegen/fn.rs
@@ -17,27 +17,39 @@ impl TryToTokens for NapiFn {
     let receiver_ret_name = Ident::new("_ret", Span::call_site());
     let ret = self.gen_fn_return(&receiver_ret_name);
     let register = self.gen_fn_register();
-
     let attrs = &self.attrs;
-    let function_call_tokens = if args_len == 0 && self.fn_self.is_none() {
+
+    let native_call = if !self.is_async {
       quote! {
-        {
-          let #receiver_ret_name = #receiver();
-          #ret
-        }
+        let #receiver_ret_name = {
+          #receiver(#(#arg_names),*)
+        };
+        #ret
       }
     } else {
+      let call = if self.is_ret_result {
+        quote! { #receiver(#(#arg_names),*).await }
+      } else {
+        quote! { Ok(#receiver(#(#arg_names),*).await) }
+      };
       quote! {
-        CallbackInfo::<#args_len>::new(env, cb, None).and_then(|mut cb| {
-          #(#arg_conversions)*
-          let #receiver_ret_name = {
-            #receiver(#(#arg_names),*)
-          };
-
+        execute_tokio_future(env, async { #call }, |env, #receiver_ret_name| {
           #ret
         })
       }
     };
+
+    let function_call = if args_len == 0 && self.fn_self.is_none() {
+      quote! { #native_call }
+    } else {
+      quote! {
+        CallbackInfo::<#args_len>::new(env, cb, None).and_then(|mut cb| {
+          #(#arg_conversions)*
+          #native_call
+        })
+      }
+    };
+
     (quote! {
       #(#attrs)*
       #[doc(hidden)]
@@ -48,7 +60,7 @@ impl TryToTokens for NapiFn {
         cb: sys::napi_callback_info
       ) -> sys::napi_value {
         unsafe {
-          #function_call_tokens.unwrap_or_else(|e| {
+          #function_call.unwrap_or_else(|e| {
             JsError::from(e).throw_into(env);
             std::ptr::null_mut::<sys::napi_value__>()
           })
@@ -120,12 +132,12 @@ impl NapiFn {
         ..
       }) => {
         quote! {
-          let #arg_name = unsafe { <#elem as FromNapiMutRef>::from_napi_mut_ref(env, cb.get_arg(#index))? };
+          let #arg_name = <#elem as FromNapiMutRef>::from_napi_mut_ref(env, cb.get_arg(#index))?;
         }
       }
       syn::Type::Reference(syn::TypeReference { elem, .. }) => {
         quote! {
-          let #arg_name = unsafe { <#elem as FromNapiRef>::from_napi_ref(env, cb.get_arg(#index))? };
+          let #arg_name = <#elem as FromNapiRef>::from_napi_ref(env, cb.get_arg(#index))?;
         }
       }
       _ => {
@@ -138,7 +150,7 @@ impl NapiFn {
         };
 
         quote! {
-          let #arg_name = unsafe {
+          let #arg_name = {
             #type_check
             <#ty as FromNapiValue>::from_napi_value(env, cb.get_arg(#index))?
           };
@@ -212,18 +224,23 @@ impl NapiFn {
 
   fn gen_fn_return(&self, ret: &Ident) -> TokenStream {
     let js_name = &self.js_name;
-    let ret_ty = &self.ret;
 
-    if let Some((ref ty, is_result)) = ret_ty {
+    if let Some(ty) = &self.ret {
       if self.kind == FnKind::Constructor {
         quote! { cb.construct(#js_name, #ret) }
-      } else if *is_result {
-        quote! {
-          if #ret.is_ok() {
+      } else if self.is_ret_result {
+        if self.is_async {
+          quote! {
             <#ty as ToNapiValue>::to_napi_value(env, #ret)
-          } else {
-            JsError::from(#ret.unwrap_err()).throw_into(env);
-            Ok(std::ptr::null_mut())
+          }
+        } else {
+          quote! {
+            if #ret.is_ok() {
+              <Result<#ty> as ToNapiValue>::to_napi_value(env, #ret)
+            } else {
+              JsError::from(#ret.unwrap_err()).throw_into(env);
+              Ok(std::ptr::null_mut())
+            }
           }
         }
       } else {
diff --git a/crates/backend/src/typegen.rs b/crates/backend/src/typegen.rs
index 33ebe7c3..f2404e8f 100644
--- a/crates/backend/src/typegen.rs
+++ b/crates/backend/src/typegen.rs
@@ -54,6 +54,8 @@ static KNOWN_TYPES: Lazy<HashMap<&'static str, &'static str>> = Lazy::new(|| {
     ("Value", "any"),
     ("Map", "Record<string, any>"),
     ("HashMap", "Record<{}, {}>"),
+    ("Buffer", "Buffer"),
+    // TODO: Vec<u8> should be Buffer, now is Array<number>
     ("Vec", "Array<{}>"),
     ("Option", "{} | null"),
     ("Result", "Error | {}"),
diff --git a/crates/backend/src/typegen/fn.rs b/crates/backend/src/typegen/fn.rs
index 4b5358e4..32f15f39 100644
--- a/crates/backend/src/typegen/fn.rs
+++ b/crates/backend/src/typegen/fn.rs
@@ -87,8 +87,8 @@ impl NapiFn {
     match self.kind {
       FnKind::Constructor | FnKind::Setter => "".to_owned(),
       _ => {
-        let ret = if let Some((ref ret, is_result)) = self.ret {
-          let ts_type = ty_to_ts_type(ret, is_result);
+        let ret = if let Some(ret) = &self.ret {
+          let ts_type = ty_to_ts_type(ret, true);
           if ts_type == "undefined" {
             "void".to_owned()
           } else {
diff --git a/crates/macro/src/parser/mod.rs b/crates/macro/src/parser/mod.rs
index 1dccac7d..69f3315c 100644
--- a/crates/macro/src/parser/mod.rs
+++ b/crates/macro/src/parser/mod.rs
@@ -194,7 +194,7 @@ fn extract_path_ident(path: &syn::Path) -> BindgenResult<Ident> {
   }
 }
 
-fn extract_fn_types(
+fn extract_callback_trait_types(
   arguments: &syn::PathArguments,
 ) -> BindgenResult<(Vec<syn::Type>, Option<syn::Type>)> {
   match arguments {
@@ -209,39 +209,14 @@ fn extract_fn_types(
       let ret = match &arguments.output {
         syn::ReturnType::Type(_, ret_ty) => {
           let ret_ty = &**ret_ty;
-          match ret_ty {
-            syn::Type::Path(syn::TypePath {
-              qself: None,
-              ref path,
-            }) if path.segments.len() == 1 => {
-              let segment = path.segments.first().unwrap();
-
-              if segment.ident != "Result" {
-                bail_span!(ret_ty, "The return type of callback can only be `Result`");
-              } else {
-                match &segment.arguments {
-                  syn::PathArguments::AngleBracketed(syn::AngleBracketedGenericArguments {
-                    args,
-                    ..
-                  }) => {
-                    // fast test
-                    if args.to_token_stream().to_string() == "()" {
-                      None
-                    } else {
-                      let ok_arg = args.first().unwrap();
-                      match ok_arg {
-                        syn::GenericArgument::Type(ty) => Some(ty.clone()),
-                        _ => bail_span!(ok_arg, "unsupported generic type"),
-                      }
-                    }
-                  }
-                  _ => {
-                    bail_span!(segment, "Too many arguments")
-                  }
-                }
-              }
+          if let Some(ty_of_result) = extract_result_ty(ret_ty)? {
+            if ty_of_result.to_token_stream().to_string() == "()" {
+              None
+            } else {
+              Some(ty_of_result)
             }
-            _ => bail_span!(ret_ty, "The return type of callback can only be `Result`"),
+          } else {
+            bail_span!(ret_ty, "The return type of callback can only be `Result`");
           }
         }
         _ => {
@@ -257,6 +232,34 @@ fn extract_fn_types(
   }
 }
 
+fn extract_result_ty(ty: &syn::Type) -> BindgenResult<Option<syn::Type>> {
+  match ty {
+    syn::Type::Path(syn::TypePath { qself: None, path }) if path.segments.len() == 1 => {
+      let segment = path.segments.first().unwrap();
+
+      if segment.ident != "Result" {
+        Ok(None)
+      } else {
+        match &segment.arguments {
+          syn::PathArguments::AngleBracketed(syn::AngleBracketedGenericArguments {
+            args, ..
+          }) => {
+            let ok_arg = args.first().unwrap();
+            match ok_arg {
+              syn::GenericArgument::Type(ty) => Ok(Some(ty.clone())),
+              _ => bail_span!(ok_arg, "unsupported generic type"),
+            }
+          }
+          _ => {
+            bail_span!(segment, "unsupported generic type")
+          }
+        }
+      }
+    }
+    _ => Ok(None),
+  }
+}
+
 fn get_expr(mut expr: &syn::Expr) -> &syn::Expr {
   while let syn::Expr::Group(g) = expr {
     expr = &g.expr;
@@ -480,7 +483,7 @@ fn napi_fn_from_decl(
       syn::FnArg::Typed(mut p) => {
         let ty_str = p.ty.to_token_stream().to_string();
         if let Some(path_arguments) = callback_traits.get(&ty_str) {
-          match extract_fn_types(path_arguments) {
+          match extract_callback_trait_types(path_arguments) {
             Ok((fn_args, fn_ret)) => Some(NapiFnArgKind::Callback(Box::new(CallbackArg {
               pat: p.pat,
               args: fn_args,
@@ -518,11 +521,15 @@ fn napi_fn_from_decl(
     })
     .collect::<Vec<_>>();
 
-  let ret = match output {
-    syn::ReturnType::Default => None,
+  let (ret, is_ret_result) = match output {
+    syn::ReturnType::Default => (None, false),
     syn::ReturnType::Type(_, ty) => {
-      let is_result = ty.to_token_stream().to_string().starts_with("Result <");
-      Some((replace_self(*ty, parent), is_result))
+      let result_ty = extract_result_ty(&ty)?;
+      if result_ty.is_some() {
+        (result_ty, true)
+      } else {
+        (Some(replace_self(*ty, parent)), false)
+      }
     }
   };
 
@@ -559,6 +566,7 @@ fn napi_fn_from_decl(
       js_name,
       args,
       ret,
+      is_ret_result,
       is_async: asyncness.is_some(),
       vis,
       kind: fn_kind(opts),
diff --git a/crates/napi/Cargo.toml b/crates/napi/Cargo.toml
index e0125ef0..cc570512 100644
--- a/crates/napi/Cargo.toml
+++ b/crates/napi/Cargo.toml
@@ -23,6 +23,8 @@ napi7 = ["napi6", "napi-sys/napi7"]
 napi8 = ["napi7", "napi-sys/napi8"]
 serde-json = ["serde", "serde_json"]
 tokio_rt = ["tokio", "once_cell", "napi4"]
+async = ["tokio_rt"]
+full = ["latin1", "napi8", "async", "serde-json"]
 
 [dependencies]
 ctor = "0.1"
diff --git a/crates/napi/src/bindgen_runtime/js_values/buffer.rs b/crates/napi/src/bindgen_runtime/js_values/buffer.rs
index 6b0c54cd..697d4bbd 100644
--- a/crates/napi/src/bindgen_runtime/js_values/buffer.rs
+++ b/crates/napi/src/bindgen_runtime/js_values/buffer.rs
@@ -103,3 +103,9 @@ impl ValidateNapiValue for Buffer {
     vec![ValueType::Object]
   }
 }
+
+impl ToNapiValue for Vec<u8> {
+  unsafe fn to_napi_value(env: sys::napi_env, val: Self) -> Result<sys::napi_value> {
+    Buffer::to_napi_value(env, val.into())
+  }
+}
diff --git a/crates/napi/src/lib.rs b/crates/napi/src/lib.rs
index 3782ca88..dbb2e32f 100644
--- a/crates/napi/src/lib.rs
+++ b/crates/napi/src/lib.rs
@@ -158,6 +158,7 @@ macro_rules! assert_type_of {
 pub mod bindgen_prelude {
   #[cfg(feature = "compat-mode")]
   pub use crate::bindgen_runtime::register_module_exports;
+  pub use crate::tokio_runtime::*;
   pub use crate::{
     assert_type_of, bindgen_runtime::*, check_status, check_status_or_throw, error, error::*, sys,
     type_of, JsError, Property, PropertyAttributes, Result, Status, Task, ValueType,
diff --git a/examples/napi/Cargo.toml b/examples/napi/Cargo.toml
index f864ae91..1a4f8478 100644
--- a/examples/napi/Cargo.toml
+++ b/examples/napi/Cargo.toml
@@ -13,10 +13,12 @@ napi3 = ["napi/napi3"]
 
 [dependencies]
 napi-derive = { path = "../../crates/macro", features = ["type-def"] }
-napi = { path = "../../crates/napi", features = ["latin1", "serde-json"] }
+napi = { path = "../../crates/napi", features = ["full"] }
 serde = "1"
 serde_derive = "1"
 serde_json = "1"
+tokio = {version = "1", features = ["default", "fs"]}
+futures = "0.3"
 
 [build-dependencies]
 napi-build = { path = "../../crates/build" }
\ No newline at end of file
diff --git a/examples/napi/__test__/typegen.spec.ts.md b/examples/napi/__test__/typegen.spec.ts.md
index b08ac600..1c4cc031 100644
--- a/examples/napi/__test__/typegen.spec.ts.md
+++ b/examples/napi/__test__/typegen.spec.ts.md
@@ -11,6 +11,7 @@ Generated by [AVA](https://avajs.dev).
     `export function getWords(): Array<string>␊
     export function getNums(): Array<number>␊
     export function sumNums(nums: Array<number>): number␊
+    export function readFileAsync(path: string): Promise<Array<number>>␊
     export function getCwd(callback: (arg0: string) => void): void␊
     export function readFile(callback: (arg0: Error | undefined, arg1: string | null) => void): void␊
     export enum Kind { Dog = 0, Cat = 1, Duck = 2 }␊
diff --git a/examples/napi/__test__/typegen.spec.ts.snap b/examples/napi/__test__/typegen.spec.ts.snap
index cc5d8229..3c0ac156 100644
Binary files a/examples/napi/__test__/typegen.spec.ts.snap and b/examples/napi/__test__/typegen.spec.ts.snap differ
diff --git a/examples/napi/__test__/values.spec.ts b/examples/napi/__test__/values.spec.ts
index ed0823e4..fca2a6a8 100644
--- a/examples/napi/__test__/values.spec.ts
+++ b/examples/napi/__test__/values.spec.ts
@@ -1,3 +1,5 @@
+import { join } from 'path'
+
 import test from 'ava'
 
 import {
@@ -23,6 +25,7 @@ import {
   readPackageJson,
   getPackageJsonName,
   getBuffer,
+  readFileAsync,
 } from '../'
 
 test('number', (t) => {
@@ -117,3 +120,13 @@ test('serde-json', (t) => {
 test('buffer', (t) => {
   t.is(getBuffer().toString('utf-8'), 'Hello world')
 })
+
+test('async', async (t) => {
+  const bufPromise = readFileAsync(join(__dirname, '../package.json'))
+  await t.notThrowsAsync(bufPromise)
+  const buf = await bufPromise
+  const { name } = JSON.parse(buf.toString())
+  t.is(name, 'napi-examples')
+
+  await t.throwsAsync(() => readFileAsync('some_nonexist_path.file'))
+})
diff --git a/examples/napi/index.d.ts b/examples/napi/index.d.ts
index e7104db4..a6331520 100644
--- a/examples/napi/index.d.ts
+++ b/examples/napi/index.d.ts
@@ -1,6 +1,7 @@
 export function getWords(): Array<string>
 export function getNums(): Array<number>
 export function sumNums(nums: Array<number>): number
+export function readFileAsync(path: string): Promise<Array<number>>
 export function getCwd(callback: (arg0: string) => void): void
 export function readFile(callback: (arg0: Error | undefined, arg1: string | null) => void): void
 export enum Kind { Dog = 0, Cat = 1, Duck = 2 }
diff --git a/examples/napi/src/async.rs b/examples/napi/src/async.rs
new file mode 100644
index 00000000..7822cf7b
--- /dev/null
+++ b/examples/napi/src/async.rs
@@ -0,0 +1,17 @@
+use futures::prelude::*;
+use napi::bindgen_prelude::*;
+use tokio::fs;
+
+#[napi]
+async fn read_file_async(path: String) -> Result<Vec<u8>> {
+  fs::read(path)
+    .map(|v| {
+      v.map_err(|e| {
+        Error::new(
+          Status::GenericFailure,
+          format!("failed to read file, {}", e),
+        )
+      })
+    })
+    .await
+}
diff --git a/examples/napi/src/lib.rs b/examples/napi/src/lib.rs
index e1a3699b..057d6756 100644
--- a/examples/napi/src/lib.rs
+++ b/examples/napi/src/lib.rs
@@ -4,6 +4,7 @@ extern crate napi_derive;
 extern crate serde_derive;
 
 mod array;
+mod r#async;
 mod callback;
 mod class;
 mod r#enum;