diff --git a/Cargo.lock b/Cargo.lock
index 21f5b45cea..5ce4568a10 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -419,6 +419,7 @@ version = "0.1.0"
 dependencies = [
  "codechain-core 0.1.0",
  "codechain-key 0.1.0",
+ "codechain-keystore 0.1.0",
  "codechain-logger 0.1.0",
  "codechain-network 0.1.0",
  "codechain-state 0.1.0",
diff --git a/keystore/src/error.rs b/keystore/src/error.rs
index b1d5b4cb31..b9782e945e 100644
--- a/keystore/src/error.rs
+++ b/keystore/src/error.rs
@@ -37,6 +37,8 @@ pub enum Error {
     InvalidKeyFile(String),
     /// Account creation failed.
     CreationFailed,
+    /// Account already exists.
+    AlreadyExists,
     /// `ckeys` error
     CKey(CKeyError),
     /// `CCrypto` error
@@ -55,6 +57,7 @@ impl fmt::Display for Error {
             Error::InvalidMessage => "Invalid message".into(),
             Error::InvalidKeyFile(ref reason) => format!("Invalid key file: {}", reason),
             Error::CreationFailed => "Account creation failed".into(),
+            Error::AlreadyExists => "Account already exists".into(),
             Error::CKey(ref err) => err.to_string(),
             Error::CCrypto(ref err) => err.to_string(),
             Error::Custom(ref s) => s.clone(),
diff --git a/keystore/src/keystore.rs b/keystore/src/keystore.rs
index 2666d38674..96e0440de7 100644
--- a/keystore/src/keystore.rs
+++ b/keystore/src/keystore.rs
@@ -64,7 +64,11 @@ impl KeyStore {
 
 impl SimpleSecretStore for KeyStore {
     fn insert_account(&self, secret: Secret, password: &Password) -> Result<Address, Error> {
-        self.store.insert_account(secret, password)
+        let keypair = KeyPair::from_private(secret.into()).map_err(|_| Error::CreationFailed)?;
+        match self.has_account(&keypair.address())? {
+            true => Err(Error::AlreadyExists),
+            false => self.store.insert_account(secret, password),
+        }
     }
 
     fn accounts(&self) -> Result<Vec<Address>, Error> {
@@ -345,10 +349,10 @@ impl SimpleSecretStore for KeyMultiStore {
     }
 
     fn has_account(&self, account: &Address) -> Result<bool, Error> {
-        let mut accounts = self.get_accounts(account)?.into_iter();
-        match accounts.next() {
-            Some(_) => Ok(true),
-            None => Ok(false),
+        match self.get_accounts(account) {
+            Ok(_) => Ok(true),
+            Err(Error::InvalidAccount) => Ok(false),
+            Err(e) => Err(e),
         }
     }
 
diff --git a/rpc/Cargo.toml b/rpc/Cargo.toml
index 60b7aec82e..e4b4510156 100644
--- a/rpc/Cargo.toml
+++ b/rpc/Cargo.toml
@@ -8,6 +8,7 @@ authors = ["CodeChain Team <codechain@kodebox.io>"]
 [dependencies]
 codechain-core = { path = "../core" }
 codechain-key = { path = "../key" }
+codechain-keystore = { path = "../keystore" }
 codechain-logger = { path = "../util/logger" }
 codechain-network = { path = "../network" }
 codechain-state = { path = "../state" }
diff --git a/rpc/src/lib.rs b/rpc/src/lib.rs
index 84f47de00d..5086edddee 100644
--- a/rpc/src/lib.rs
+++ b/rpc/src/lib.rs
@@ -18,6 +18,7 @@ extern crate codechain_core as ccore;
 #[macro_use]
 extern crate codechain_logger as clogger;
 extern crate codechain_key as ckey;
+extern crate codechain_keystore as ckeystore;
 extern crate codechain_network as cnetwork;
 extern crate codechain_state as cstate;
 extern crate codechain_types as ctypes;
diff --git a/rpc/src/v1/errors.rs b/rpc/src/v1/errors.rs
index f27d4bf0f9..33b79ed32e 100644
--- a/rpc/src/v1/errors.rs
+++ b/rpc/src/v1/errors.rs
@@ -19,6 +19,7 @@ use std::fmt;
 use ccore::AccountProviderError;
 use ccore::Error as CoreError;
 use ckey::Error as KeyError;
+use ckeystore::Error as KeystoreError;
 use cnetwork::control::Error as NetworkControlError;
 use cstate::StateError;
 use ctypes::parcel::Error as ParcelError;
@@ -43,6 +44,11 @@ mod codes {
     pub const TOO_LOW_FEE: i64 = -32033;
     pub const TOO_CHEAP_TO_REPLACE: i64 = -32034;
     pub const INVALID_NONCE: i64 = -32035;
+    pub const KEYSTORE_ERROR: i64 = -32040;
+    pub const KEY_ERROR: i64 = -32041;
+    pub const ALREADY_EXISTS: i64 = -32042;
+    pub const WRONG_PASSWORD: i64 = -32043;
+    pub const NO_SUCH_ACCOUNT: i64 = -32044;
     pub const UNKNOWN_ERROR: i64 = -32099;
 }
 
@@ -148,10 +154,39 @@ pub fn rlp(error: DecoderError) -> Error {
 }
 
 pub fn account_provider(error: AccountProviderError) -> Error {
-    Error {
-        code: ErrorCode::ServerError(codes::ACCOUNT_PROVIDER_ERROR),
-        message: "AccountProvider error".into(),
-        data: Some(Value::String(format!("{:?}", error))),
+    match error {
+        AccountProviderError::KeystoreError(error) => match error {
+            KeystoreError::InvalidAccount => Error {
+                code: ErrorCode::ServerError(codes::NO_SUCH_ACCOUNT),
+                message: "No Such Account".into(),
+                data: Some(Value::String(format!("{:?}", error))),
+            },
+            KeystoreError::InvalidPassword => Error {
+                code: ErrorCode::ServerError(codes::WRONG_PASSWORD),
+                message: "Wrong Password".into(),
+                data: Some(Value::String(format!("{:?}", error))),
+            },
+            KeystoreError::AlreadyExists => Error {
+                code: ErrorCode::ServerError(codes::ALREADY_EXISTS),
+                message: "Already Exists".into(),
+                data: Some(Value::String(format!("{:?}", error))),
+            },
+            _ => Error {
+                code: ErrorCode::ServerError(codes::KEYSTORE_ERROR),
+                message: "Keystore Error".into(),
+                data: Some(Value::String(format!("{:?}", error))),
+            },
+        },
+        AccountProviderError::KeyError(_) => Error {
+            code: ErrorCode::ServerError(codes::KEY_ERROR),
+            message: "Key Error".into(),
+            data: Some(Value::String(format!("{:?}", error))),
+        },
+        _ => Error {
+            code: ErrorCode::ServerError(codes::ACCOUNT_PROVIDER_ERROR),
+            message: "AccountProvider Error".into(),
+            data: Some(Value::String(format!("{:?}", error))),
+        },
     }
 }