diff --git a/command.go b/command.go
index dd288f3bf..ba8c140f6 100644
--- a/command.go
+++ b/command.go
@@ -8,6 +8,7 @@ package main
 import (
 	"github.com/benbjohnson/go-raft"
 	"encoding/json"
+	"time"
 	)
 
 // A command represents an action to be taken on the replicated state machine.
@@ -34,7 +35,7 @@ func (c *SetCommand) CommandName() string {
 
 // Set the value of key to value
 func (c *SetCommand) Apply(server *raft.Server) ([]byte, error) {
-	res := s.Set(c.Key, c.Value)
+	res := s.Set(c.Key, c.Value, time.Unix(0, 0))
 	return json.Marshal(res)
 }
 
diff --git a/store.go b/store.go
index d26554169..dabbc2a54 100644
--- a/store.go
+++ b/store.go
@@ -3,26 +3,35 @@ package main
 import (
 	"path"
 	"encoding/json"
+	"time"
+	"fmt"
 	)
 
 // CONSTANTS
 const (
 	ERROR = -1 + iota
 	SET 
-	GET
 	DELETE
+	GET
 )
 
 type Store struct {
-	Nodes map[string]string  `json:"nodes"`
+	Nodes map[string]Node  `json:"nodes"`
+}
+
+type Node struct {
+	Value string
+	ExpireTime time.Time
+	update chan time.Time
 }
 
 type Response struct {
-	Action	 int    `json:action`
-	Key      string `json:key`
-	OldValue string `json:oldValue`
-	NewValue string `json:newValue`
-	Exist 	 bool `json:exist`
+	Action	 int    `json:"action"`
+	Key      string `json:"key"`
+	OldValue string `json:"oldValue"`
+	NewValue string `json:"newValue"`
+	Exist 	 bool `json:"exist"`
+	Expiration time.Time `json:"expiration"`
 }
 
 
@@ -36,25 +45,75 @@ func init() {
 // make a new stroe
 func createStore() *Store{
 	s := new(Store)
-	s.Nodes = make(map[string]string)
+	s.Nodes = make(map[string]Node)
 	return s
 }
 
 // set the key to value, return the old value if the key exists 
-func (s *Store) Set(key string, value string) Response {
+func (s *Store) Set(key string, value string, expireTime time.Time) Response {
+
 	key = path.Clean(key)
 
-	oldValue, ok := s.Nodes[key]
+	var expire bool = false
+
+	expire = !expireTime.Equal(time.Unix(0,0))
+
+	// when the slow follower receive the set command
+	// the key may be expired, we need also to delete 
+	// the previous value of key
+	if expire && expireTime.Sub(time.Now()) < 0 {
+		return s.Delete(key)
+	}
+
+	node, ok := s.Nodes[key]
 
 	if ok {
-		s.Nodes[key] = value
-		w.notify(SET, key, oldValue, value, true)
-		return Response{SET, key, oldValue, value, true}
+		update := make(chan time.Time)
+		s.Nodes[key] = Node{value, expireTime, update}
+		w.notify(SET, key, node.Value, value, true)
+
+		// node is not permanent before
+		if !node.ExpireTime.Equal(time.Unix(0,0)) {
+				node.update <- expireTime
+		} else {
+			// if current node is not permanent
+			if expire {
+				go s.expire(key, update, expireTime)
+			}
+		}
+
+		return Response{SET, key, node.Value, value, true, time.Unix(0, 0)}
 
 	} else {
-		s.Nodes[key] = value
+		update := make(chan time.Time)
+		s.Nodes[key] = Node{value, expireTime, update}
 		w.notify(SET, key, "", value, false)
-		return Response{SET, key, "", value, false}
+		if expire {
+			go s.expire(key, update, expireTime)
+		}
+		return Response{SET, key, "", value, false, time.Unix(0, 0)}
+	}
+}
+
+// delete the key when it expires
+func (s *Store) expire(key string, update chan time.Time, expireTime time.Time) {
+	duration := expireTime.Sub(time.Now())
+
+	for {
+		select {
+		// timeout delte key
+		case <-time.After(duration):
+			fmt.Println("expired at ", time.Now())
+			s.Delete(key)
+			return
+		case updateTime := <-update:
+			//update duration
+			if updateTime.Equal(time.Unix(0,0)) {
+				fmt.Println("node became stable")
+				return
+			}
+			duration = updateTime.Sub(time.Now())
+		}
 	}
 }
 
@@ -62,12 +121,12 @@ func (s *Store) Set(key string, value string) Response {
 func (s *Store) Get(key string) Response {
 	key = path.Clean(key)
 
-	value, ok := s.Nodes[key]
+	node, ok := s.Nodes[key]
 
 	if ok {
-		return Response{GET, key, value, value, true}
+		return Response{GET, key, node.Value, node.Value, true, node.ExpireTime}
 	} else {
-		return Response{GET, key, "", value, false}
+		return Response{GET, key, "", "", false, time.Unix(0, 0)}
 	}
 }
 
@@ -75,16 +134,16 @@ func (s *Store) Get(key string) Response {
 func (s *Store) Delete(key string) Response {
 	key = path.Clean(key)
 
-	oldValue, ok := s.Nodes[key]
+	node, ok := s.Nodes[key]
 
 	if ok {
 		delete(s.Nodes, key)
 
-		w.notify(DELETE, key, oldValue, "", true)
+		w.notify(DELETE, key, node.Value, "", true)
 
-		return Response{DELETE, key, oldValue, "", true}
+		return Response{DELETE, key, node.Value, "", true, node.ExpireTime}
 	} else {
-		return Response{DELETE, key, "", "", false}
+		return Response{DELETE, key, "", "", false, time.Unix(0, 0)}
 	}
 }
 
diff --git a/store_test.go b/store_test.go
index 705b901f9..6d1f77e10 100644
--- a/store_test.go
+++ b/store_test.go
@@ -2,29 +2,31 @@ package main
 
 import (
 	"testing"
+	"time"
+	"fmt"
 )
 
 func TestStoreGet(t *testing.T) {
 
-	s.Set("foo", "bar")
+	s.Set("foo", "bar", time.Unix(0, 0))
 
-	value, err := s.Get("foo")
+	res := s.Get("foo")
 
-	if err!= nil || value != "bar" {
+	if res.NewValue != "bar" {
 		t.Fatalf("Cannot get stored value")
 	}
 
 	s.Delete("foo")
-	value, err = s.Get("foo")
+	res = s.Get("foo")
 
-	if err == nil{
+	if res.Exist {
 		t.Fatalf("Got deleted value")
 	}
 }
 
 func TestSaveAndRecovery(t *testing.T) {
 
-	s.Set("foo", "bar")
+	s.Set("foo", "bar", time.Unix(0, 0))
 
 	state, err := s.Save()
 
@@ -35,10 +37,78 @@ func TestSaveAndRecovery(t *testing.T) {
 	newStore := createStore()
 	newStore.Recovery(state)
 
-	value, err := newStore.Get("foo")
+	res := newStore.Get("foo")
 
-	if err!= nil || value != "bar" {
+	if res.OldValue != "bar" {
 		t.Fatalf("Cannot recovery")
 	}
+	s.Delete("foo")
+
+}
+
+func TestExpire(t *testing.T) {
+	fmt.Println(time.Now())
+	fmt.Println("TEST EXPIRE")
+
+	// test expire
+	s.Set("foo", "bar", time.Now().Add(time.Second * 1))
+	time.Sleep(2*time.Second)
+
+	res := s.Get("foo")
+
+	if res.Exist {
+		t.Fatalf("Got expired value")
+	}
+
+	//test change expire time
+	s.Set("foo", "bar", time.Now().Add(time.Second * 10))
+
+	res = s.Get("foo")
+
+	if !res.Exist {
+		t.Fatalf("Cannot get Value")
+	}
+
+	s.Set("foo", "barbar", time.Now().Add(time.Second * 1))
+
+	time.Sleep(2 * time.Second)
+
+	res = s.Get("foo")
+
+	if res.Exist {
+		t.Fatalf("Got expired value")
+	}
+
+
+	// test change expire to stable
+	s.Set("foo", "bar", time.Now().Add(time.Second * 1))
+
+	s.Set("foo", "bar", time.Unix(0,0))
+
+	time.Sleep(2*time.Second)
+
+	res = s.Get("foo")
+
+	if !res.Exist {
+		t.Fatalf("Cannot get Value")
+	}
+
+	// test stable to expire 
+	s.Set("foo", "bar", time.Now().Add(time.Second * 1))
+	time.Sleep(2*time.Second)
+	res = s.Get("foo")
+
+	if res.Exist {
+		t.Fatalf("Got expired value")
+	}
+
+	// test set older node 
+	s.Set("foo", "bar", time.Now().Add(-time.Second * 1))
+	res = s.Get("foo")
+
+	if res.Exist {
+		t.Fatalf("Got expired value")
+	}
+
 
 }
diff --git a/watcher.go b/watcher.go
index 43682b696..f766ea84f 100644
--- a/watcher.go
+++ b/watcher.go
@@ -3,6 +3,8 @@ package main
 import (
 	"path"
 	"strings"
+	//"fmt"
+	"time"
 	)
 
 
@@ -46,20 +48,18 @@ func (w *Watcher) add(prefix string, c chan Response) error {
 func (w *Watcher) notify(action int, key string, oldValue string, newValue string, exist bool) error {
 	key = path.Clean(key)
 	segments := strings.Split(key, "/")
-
 	currPath := "/"
 
 	// walk through all the pathes
 	for _, segment := range segments {
-
-		currPath := path.Join(currPath, segment)
+		currPath = path.Join(currPath, segment)
 
 		chans, ok := w.chanMap[currPath]
 
 		if ok {
-			debug("Notify at ", currPath)
+			debug("Notify at %s", currPath)
 
-			n := Response {action, key, oldValue, newValue, exist}
+			n := Response {action, key, oldValue, newValue, exist, time.Unix(0, 0)}
 
 			// notify all the watchers
 			for _, c := range chans {
diff --git a/watcher_test.go b/watcher_test.go
index f7197eb9c..f6da49719 100644
--- a/watcher_test.go
+++ b/watcher_test.go
@@ -3,23 +3,24 @@ package main
 import (
 	"testing"
 	"fmt"
+	"time"
 )
 
 func TestWatch(t *testing.T) {
 	// watcher := createWatcher()
-	c := make(chan Notification)
-	d := make(chan Notification)
+	c := make(chan Response)
+	d := make(chan Response)
 	w.add("/", c)
 	go say(c)
 	w.add("/prefix/", d)
 	go say(d)
-	s.Set("/prefix/foo", "bar")
+	s.Set("/prefix/foo", "bar", time.Unix(0, 0))
 }
 
-func say(c chan Notification) {
+func say(c chan Response) {
 	result := <-c
 
-	if result.action != -1 {
+	if result.Action != -1 {
 		fmt.Println("yes")
 	} else {
 		fmt.Println("no")