diff --git a/cluster.go b/cluster.go
index ac461d5b9..204f507bd 100644
--- a/cluster.go
+++ b/cluster.go
@@ -48,21 +48,23 @@ import (
 
 type mongoCluster struct {
 	sync.RWMutex
-	serverSynced sync.Cond
-	userSeeds    []string
-	dynaSeeds    []string
-	servers      mongoServers
-	masters      mongoServers
-	references   int
-	syncing      bool
-	direct       bool
-	failFast     bool
-	syncCount    uint
-	setName      string
-	cachedIndex  map[string]bool
-	sync         chan bool
-	dial         dialer
-	appName      string
+	serverSynced  sync.Cond
+	userSeeds     []string
+	dynaSeeds     []string
+	servers       mongoServers
+	masters       mongoServers
+	references    int
+	syncing       bool
+	direct        bool
+	failFast      bool
+	syncCount     uint
+	setName       string
+	cachedIndex   map[string]bool
+	sync          chan bool
+	dial          dialer
+	appName       string
+	minPoolSize   int
+	maxIdleTimeMS int
 }
 
 func newCluster(userSeeds []string, direct, failFast bool, dial dialer, setName string, appName string) *mongoCluster {
@@ -437,11 +439,13 @@ func (cluster *mongoCluster) syncServersLoop() {
 func (cluster *mongoCluster) server(addr string, tcpaddr *net.TCPAddr) *mongoServer {
 	cluster.RLock()
 	server := cluster.servers.Search(tcpaddr.String())
+	minPoolSize := cluster.minPoolSize
+	maxIdleTimeMS := cluster.maxIdleTimeMS
 	cluster.RUnlock()
 	if server != nil {
 		return server
 	}
-	return newServer(addr, tcpaddr, cluster.sync, cluster.dial)
+	return newServer(addr, tcpaddr, cluster.sync, cluster.dial, minPoolSize, maxIdleTimeMS)
 }
 
 func resolveAddr(addr string) (*net.TCPAddr, error) {
diff --git a/server.go b/server.go
index 7ad955255..f999b2407 100644
--- a/server.go
+++ b/server.go
@@ -55,6 +55,8 @@ type mongoServer struct {
 	pingCount     uint32
 	closed        bool
 	abended       bool
+	minPoolSize   int
+	maxIdleTimeMS int
 }
 
 type dialer struct {
@@ -76,17 +78,22 @@ type mongoServerInfo struct {
 
 var defaultServerInfo mongoServerInfo
 
-func newServer(addr string, tcpaddr *net.TCPAddr, sync chan bool, dial dialer) *mongoServer {
+func newServer(addr string, tcpaddr *net.TCPAddr, sync chan bool, dial dialer, minPoolSize, maxIdleTimeMS int) *mongoServer {
 	server := &mongoServer{
-		Addr:         addr,
-		ResolvedAddr: tcpaddr.String(),
-		tcpaddr:      tcpaddr,
-		sync:         sync,
-		dial:         dial,
-		info:         &defaultServerInfo,
-		pingValue:    time.Hour, // Push it back before an actual ping.
+		Addr:          addr,
+		ResolvedAddr:  tcpaddr.String(),
+		tcpaddr:       tcpaddr,
+		sync:          sync,
+		dial:          dial,
+		info:          &defaultServerInfo,
+		pingValue:     time.Hour, // Push it back before an actual ping.
+		minPoolSize:   minPoolSize,
+		maxIdleTimeMS: maxIdleTimeMS,
 	}
 	go server.pinger(true)
+	if maxIdleTimeMS != 0 {
+		go server.poolShrinker()
+	}
 	return server
 }
 
@@ -221,6 +228,7 @@ func (server *mongoServer) close(waitForIdle bool) {
 func (server *mongoServer) RecycleSocket(socket *mongoSocket) {
 	server.Lock()
 	if !server.closed {
+		socket.lastTimeUsed = time.Now()
 		server.unusedSockets = append(server.unusedSockets, socket)
 	}
 	server.Unlock()
@@ -346,6 +354,53 @@ func (server *mongoServer) pinger(loop bool) {
 	}
 }
 
+func (server *mongoServer) poolShrinker() {
+	ticker := time.NewTicker(1 * time.Minute)
+	for _ = range ticker.C {
+		if server.closed {
+			ticker.Stop()
+			return
+		}
+		server.Lock()
+		unused := len(server.unusedSockets)
+		if unused < server.minPoolSize {
+			server.Unlock()
+			continue
+		}
+		now := time.Now()
+		end := 0
+		reclaimMap := map[*mongoSocket]struct{}{}
+		// Because the acquisition and recycle are done at the tail of array,
+		// the head is always the oldest unused socket.
+		for _, s := range server.unusedSockets[:unused-server.minPoolSize] {
+			if s.lastTimeUsed.Add(time.Duration(server.maxIdleTimeMS) * time.Millisecond).After(now) {
+				break
+			}
+			end++
+			reclaimMap[s] = struct{}{}
+		}
+		tbr := server.unusedSockets[:end]
+		if end > 0 {
+			next := make([]*mongoSocket, unused-end)
+			copy(next, server.unusedSockets[end:])
+			server.unusedSockets = next
+			remainSockets := []*mongoSocket{}
+			for _, s := range server.liveSockets {
+				if _, ok := reclaimMap[s]; !ok {
+					remainSockets = append(remainSockets, s)
+				}
+			}
+			server.liveSockets = remainSockets
+			stats.conn(-1*end, server.info.Master)
+		}
+		server.Unlock()
+
+		for _, s := range tbr {
+			s.Close()
+		}
+	}
+}
+
 type mongoServerSlice []*mongoServer
 
 func (s mongoServerSlice) Len() int {
diff --git a/session.go b/session.go
index 561f79487..d1c88420e 100644
--- a/session.go
+++ b/session.go
@@ -271,6 +271,16 @@ const (
 //        Defines the per-server socket pool limit. Defaults to 4096.
 //        See Session.SetPoolLimit for details.
 //
+//     minPoolSize=<limit>
+//
+//        Defines the per-server socket pool minium size. Defaults to 0.
+//
+//     maxIdleTimeMS=<millisecond>
+//
+//        The maximum number of milliseconds that a connection can remain idle in the pool
+//        before being removed and closed. If maxIdleTimeMS is 0, connections will never be
+//        closed due to inactivity.
+//
 //     appName=<appName>
 //
 //        The identifier of this client application. This parameter is used to
@@ -322,6 +332,8 @@ func ParseURL(url string) (*DialInfo, error) {
 	appName := ""
 	readPreferenceMode := Primary
 	var readPreferenceTagSets []bson.D
+	minPoolSize := 0
+	maxIdleTimeMS := 0
 	for _, opt := range uinfo.options {
 		switch opt.key {
 		case "authSource":
@@ -368,6 +380,22 @@ func ParseURL(url string) (*DialInfo, error) {
 				doc = append(doc, bson.DocElem{Name: strings.TrimSpace(kvp[0]), Value: strings.TrimSpace(kvp[1])})
 			}
 			readPreferenceTagSets = append(readPreferenceTagSets, doc)
+		case "minPoolSize":
+			minPoolSize, err = strconv.Atoi(opt.value)
+			if err != nil {
+				return nil, errors.New("bad value for minPoolSize: " + opt.value)
+			}
+			if minPoolSize < 0 {
+				return nil, errors.New("bad value (negtive) for minPoolSize: " + opt.value)
+			}
+		case "maxIdleTimeMS":
+			maxIdleTimeMS, err = strconv.Atoi(opt.value)
+			if err != nil {
+				return nil, errors.New("bad value for maxIdleTimeMS: " + opt.value)
+			}
+			if maxIdleTimeMS < 0 {
+				return nil, errors.New("bad value (negtive) for maxIdleTimeMS: " + opt.value)
+			}
 		case "connect":
 			if opt.value == "direct" {
 				direct = true
@@ -402,6 +430,8 @@ func ParseURL(url string) (*DialInfo, error) {
 			TagSets: readPreferenceTagSets,
 		},
 		ReplicaSetName: setName,
+		MinPoolSize:    minPoolSize,
+		MaxIdleTimeMS:  maxIdleTimeMS,
 	}
 	return &info, nil
 }
@@ -475,6 +505,14 @@ type DialInfo struct {
 	// cluster and establish connections with further servers too.
 	Direct bool
 
+	// MinPoolSize defines The minimum number of connections in the connection pool.
+	// Defaults to 0.
+	MinPoolSize int
+
+	//The maximum number of milliseconds that a connection can remain idle in the pool
+	// before being removed and closed.
+	MaxIdleTimeMS int
+
 	// DialServer optionally specifies the dial function for establishing
 	// connections with the MongoDB servers.
 	DialServer func(addr *ServerAddr) (net.Conn, error)
@@ -554,6 +592,10 @@ func DialWithInfo(info *DialInfo) (*Session, error) {
 	if info.PoolLimit > 0 {
 		session.poolLimit = info.PoolLimit
 	}
+
+	cluster.minPoolSize = info.MinPoolSize
+	cluster.maxIdleTimeMS = info.MaxIdleTimeMS
+
 	cluster.Release()
 
 	// People get confused when we return a session that is not actually
diff --git a/session_test.go b/session_test.go
index eb2c812b3..c740af47a 100644
--- a/session_test.go
+++ b/session_test.go
@@ -30,11 +30,13 @@ import (
 	"flag"
 	"fmt"
 	"math"
+	"math/rand"
 	"os"
 	"runtime"
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -166,6 +168,90 @@ func (s *S) TestURLInvalidReadPreference(c *C) {
 	}
 }
 
+func (s *S) TestMinPoolSize(c *C) {
+	tests := []struct {
+		url  string
+		size int
+		fail bool
+	}{
+		{"localhost:40001?minPoolSize=0", 0, false},
+		{"localhost:40001?minPoolSize=1", 1, false},
+		{"localhost:40001?minPoolSize=-1", -1, true},
+		{"localhost:40001?minPoolSize=-.", 0, true},
+	}
+	for _, test := range tests {
+		info, err := mgo.ParseURL(test.url)
+		if test.fail {
+			c.Assert(err, NotNil)
+		} else {
+			c.Assert(err, IsNil)
+			c.Assert(info.MinPoolSize, Equals, test.size)
+		}
+	}
+}
+
+func (s *S) TestMaxIdleTimeMS(c *C) {
+	tests := []struct {
+		url  string
+		size int
+		fail bool
+	}{
+		{"localhost:40001?maxIdleTimeMS=0", 0, false},
+		{"localhost:40001?maxIdleTimeMS=1", 1, false},
+		{"localhost:40001?maxIdleTimeMS=-1", -1, true},
+		{"localhost:40001?maxIdleTimeMS=-.", 0, true},
+	}
+	for _, test := range tests {
+		info, err := mgo.ParseURL(test.url)
+		if test.fail {
+			c.Assert(err, NotNil)
+		} else {
+			c.Assert(err, IsNil)
+			c.Assert(info.MaxIdleTimeMS, Equals, test.size)
+		}
+	}
+}
+
+func (s *S) TestPoolShrink(c *C) {
+	if *fast {
+		c.Skip("-fast")
+	}
+	oldSocket := mgo.GetStats().SocketsAlive
+
+	session, err := mgo.Dial("localhost:40001?minPoolSize=1&maxIdleTimeMS=1000")
+	c.Assert(err, IsNil)
+	defer session.Close()
+
+	parallel := 10
+	res := make(chan error, parallel+1)
+	wg := &sync.WaitGroup{}
+	for i := 1; i < parallel; i++ {
+		wg.Add(1)
+		go func() {
+			s := session.Copy()
+			defer s.Close()
+			result := struct{}{}
+			err := s.Run("ping", &result)
+
+			//sleep random time to make the allocate and release in different sequence
+			time.Sleep(time.Duration(rand.Intn(parallel)*100) * time.Millisecond)
+			res <- err
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+	stats := mgo.GetStats()
+	c.Logf("living socket: After queries: %d, before queries: %d", stats.SocketsAlive, oldSocket)
+
+	// give some time for shrink the pool, the tick is set to 1 minute
+	c.Log("Sleeping... 1 minute to for pool shrinking")
+	time.Sleep(60 * time.Second)
+
+	stats = mgo.GetStats()
+	c.Logf("living socket: After shrinking: %d, at the beginning of the test: %d", stats.SocketsAlive, oldSocket)
+	c.Assert(stats.SocketsAlive-oldSocket > 1, Equals, false)
+}
+
 func (s *S) TestURLReadPreferenceTags(c *C) {
 	type test struct {
 		url     string
diff --git a/socket.go b/socket.go
index a9124b043..ae13e401f 100644
--- a/socket.go
+++ b/socket.go
@@ -54,6 +54,7 @@ type mongoSocket struct {
 	dead           error
 	serverInfo     *mongoServerInfo
 	closeAfterIdle bool
+	lastTimeUsed   time.Time // for time based idle socket release
 	sendMeta       sync.Once
 }