diff --git a/feed-translator.cabal b/feed-translator.cabal
--- a/feed-translator.cabal
+++ b/feed-translator.cabal
@@ -1,5 +1,5 @@
 name:                feed-translator
-version:             0.1.0.1
+version:             0.1.0.2
 synopsis:            Translate syndication feeds
 homepage:            https://github.com/dahlia/feed-translator
 bug-reports:         https://github.com/dahlia/feed-translator/issues
@@ -21,8 +21,10 @@
   build-depends:       base             >=4.7      && <4.8,
                        blaze-html       >=0.8.0.0  && <0.9.0.0,
                        blaze-markup     >=0.7      && <0.8,
+                       bytestring       >=0.10.0.0 && <0.11.0.0,
                        cmdargs          >=0.10     && <0.11,
                        containers,
+                       cryptohash       >=0.11.0   && <0.12.0,
                        feed             >=0.3.10.0 && <0.4.0.0,
                        iso639,
                        lens             >=4.5,
diff --git a/src/Main.hs b/src/Main.hs
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -1,6 +1,8 @@
 {-# LANGUAGE DeriveDataTypeable #-}
+import Data.IORef (newIORef)
 import Data.String (fromString)
 
+import qualified Data.Map.Strict as M
 import Network.Wai.Handler.Warp ( HostPreference, Port
                                 , defaultSettings, runSettings
                                 , setHost, setPort, setTimeout
@@ -26,7 +28,8 @@
                        , timeout = 30 &= typ "SECONDS"
                                       &= help "timeout in seconds [30]"
                        } &= summary "Translate syndication feeds"
-    app <- application
+    cacheMapRef <- newIORef M.empty
+    app <- application cacheMapRef
     let settings = setHost (fromString $ host args) $
                    setPort (port args) $
                    setTimeout (timeout args) defaultSettings
diff --git a/src/Web/Feed/FeedTranslator.hs b/src/Web/Feed/FeedTranslator.hs
--- a/src/Web/Feed/FeedTranslator.hs
+++ b/src/Web/Feed/FeedTranslator.hs
@@ -1,4 +1,8 @@
-module Web.Feed.FeedTranslator (Translator(..), translateFeed) where
+module Web.Feed.FeedTranslator ( TextTranslator
+                               , Translator(..)
+                               , UrlTranslator
+                               , translateFeed
+                               ) where
 
 import Control.Monad (liftM)
 import Data.Text (Text, pack, unpack)
diff --git a/src/Web/Feed/FeedTranslatorWai.hs b/src/Web/Feed/FeedTranslatorWai.hs
--- a/src/Web/Feed/FeedTranslatorWai.hs
+++ b/src/Web/Feed/FeedTranslatorWai.hs
@@ -2,12 +2,14 @@
 module Web.Feed.FeedTranslatorWai (application) where
 
 import Data.Maybe (catMaybes, listToMaybe)
+import Data.IORef (IORef, atomicModifyIORef', newIORef, readIORef)
 import Control.Monad (liftM)
 import Control.Monad.IO.Class (liftIO)
 
 import Control.Lens.Getter ((^.))
+import Data.ByteString (ByteString)
 import Data.LanguageCodes (ISO639_1, fromChars)
-import qualified Data.Map as M
+import Data.Map.Strict as M
 import qualified Data.Text as T
 import qualified Data.Text.Lazy as LT
 import Data.Text.Encoding (decodeUtf8)
@@ -25,6 +27,7 @@
                    regex, request, scottyApp, setHeader)
 
 import Web.Feed.FeedTranslator (Translator(..), translateFeed)
+import Web.Feed.FeedTranslatorCache (CacheMap, wrapTranslate)
 import Web.Feed.FeedTranslatorView (index)
 
 -- | Return the Naver Translate engine that translates text from the
@@ -65,9 +68,11 @@
             Nothing -> next
         _ -> next
 
+type CacheKey = (ISO639_1, ISO639_1)
+
 -- | WAI web application.
-application :: IO Application
-application = scottyApp $ do
+application :: IORef (M.Map CacheKey (IORef CacheMap)) -> IO Application
+application cacheMapRef = scottyApp $ do
     get "/" $
         html $ renderHtml index
     get "/query/" $ do
@@ -87,10 +92,25 @@
         scheme <- liftM LT.toStrict $ param "3"
         path <- liftM LT.toStrict $ param "4"
         query <- liftM (decodeUtf8 . rawQueryString) request
+        let cacheKey :: CacheKey
+            cacheKey = (source, target)
+        cacheMap <- liftIO $ readIORef cacheMapRef
+        cacheRef <- liftIO $ case M.lookup cacheKey cacheMap of
+            Just ref -> return ref
+            Nothing -> do
+                ref <- newIORef M.empty
+                atomicModifyIORef' cacheMapRef $ \cacheMap ->
+                    (M.insert cacheKey ref cacheMap, ref)
         let url :: String
             url = T.unpack $ T.concat [scheme, "://", path, query]
-        let translator = naverTranslator source target
-        feed <- liftIO $ translateFeedUrl translator url
+            translator :: Translator
+            translator = naverTranslator source target
+            cachedTranslator :: Translator
+            cachedTranslator = translator {
+                textTranslator = wrapTranslate cacheRef
+                                               (textTranslator translator)
+            }
+        feed <- liftIO $ translateFeedUrl cachedTranslator url
         let feedXml = LT.pack $ showElement $ xmlFeed feed
         setHeader "Content-Type" "text/xml; charset=utf8"
         raw $ LTE.encodeUtf8 feedXml