diff --git a/core/src/main/scala/org/apache/spark/api/python/PythonWorkerFactory.scala b/core/src/main/scala/org/apache/spark/api/python/PythonWorkerFactory.scala
index b25016be4bea5..8d494929c4c8c 100644
--- a/core/src/main/scala/org/apache/spark/api/python/PythonWorkerFactory.scala
+++ b/core/src/main/scala/org/apache/spark/api/python/PythonWorkerFactory.scala
@@ -40,8 +40,10 @@ private[spark] class PythonWorkerFactory(pythonExec: String, envVars: Map[String
   var daemon: Process = null
   val daemonHost = InetAddress.getByAddress(Array(127, 0, 0, 1))
   var daemonPort: Int = 0
-  var daemonWorkers = new mutable.WeakHashMap[Socket, Int]()
-  var idleWorkers = new mutable.Queue[Socket]()
+  val daemonWorkers = new mutable.WeakHashMap[Socket, Int]()
+  val idleWorkers = new mutable.Queue[Socket]()
+  var lastActivity = 0L
+  new MonitorThread().start()
 
   var simpleWorkers = new mutable.WeakHashMap[Socket, Process]()
 
@@ -52,8 +54,10 @@ private[spark] class PythonWorkerFactory(pythonExec: String, envVars: Map[String
 
   def create(): Socket = {
     if (useDaemon) {
-      if (idleWorkers.length > 0) {
-        return idleWorkers.dequeue()
+      idleWorkers.synchronized {
+        if (idleWorkers.size > 0) {
+          return idleWorkers.dequeue()
+        }
       }
       createThroughDaemon()
     } else {
@@ -203,6 +207,35 @@ private[spark] class PythonWorkerFactory(pythonExec: String, envVars: Map[String
     }
   }
 
+  /**
+   * Monitor all the idle workers, kill them after timeout.
+   */
+  private class MonitorThread extends Thread(s"Idle Worker Monitor for $pythonExec") {
+
+    setDaemon(true)
+
+    override def run() {
+      while (true) {
+        idleWorkers.synchronized {
+          if (lastActivity + IDLE_WORKER_TIMEOUT_MS < System.currentTimeMillis()) {
+            while (idleWorkers.length > 0) {
+              val worker = idleWorkers.dequeue()
+              try {
+                // the Python worker will exit after closing the socket
+                worker.close()
+              } catch {
+                case e: Exception =>
+                  logWarning("Failed to close worker socket", e)
+              }
+            }
+            lastActivity = System.currentTimeMillis()
+          }
+        }
+        Thread.sleep(10000)
+      }
+    }
+  }
+
   private def stopDaemon() {
     synchronized {
       if (useDaemon) {
@@ -242,7 +275,10 @@ private[spark] class PythonWorkerFactory(pythonExec: String, envVars: Map[String
 
   def releaseWorker(worker: Socket) {
     if (useDaemon && envVars.get("SPARK_REUSE_WORKER").isDefined) {
+      idleWorkers.synchronized {
+        lastActivity = System.currentTimeMillis()
         idleWorkers.enqueue(worker)
+      }
     } else {
       // Cleanup the worker socket. This will also cause the Python worker to exit.
       try {
@@ -257,4 +293,5 @@ private[spark] class PythonWorkerFactory(pythonExec: String, envVars: Map[String
 
 private object PythonWorkerFactory {
   val PROCESS_WAIT_TIMEOUT_MS = 10000
+  val IDLE_WORKER_TIMEOUT_MS = 60000
 }
diff --git a/python/run-tests b/python/run-tests
index f2d017ca99c8a..7b1ee3e1cddba 100755
--- a/python/run-tests
+++ b/python/run-tests
@@ -50,7 +50,7 @@ echo "Running PySpark tests. Output is in python/unit-tests.log."
 
 # Try to test with Python 2.6, since that's the minimum version that we support:
 if [ $(which python2.6) ]; then
-    export PYSPARK_PYTHON="pypy"
+    export PYSPARK_PYTHON="python2.6"
 fi
 
 echo "Testing with Python version:"