diff --git a/python/pyspark/rdd.py b/python/pyspark/rdd.py
index 04f13523b4..aa90297855 100644
--- a/python/pyspark/rdd.py
+++ b/python/pyspark/rdd.py
@@ -212,11 +212,16 @@ class RDD(object):
         self.persist(StorageLevel.MEMORY_ONLY_SER)
         return self
 
-    def persist(self, storageLevel):
+    def persist(self, storageLevel=StorageLevel.MEMORY_ONLY_SER):
         """
         Set this RDD's storage level to persist its values across operations
         after the first time it is computed. This can only be used to assign
         a new storage level if the RDD does not have a storage level set yet.
+        If no storage level is specified defaults to (C{MEMORY_ONLY_SER}).
+
+        >>> rdd = sc.parallelize(["b", "a", "c"])
+        >>> rdd.persist().is_cached
+        True
         """
         self.is_cached = True
         javaStorageLevel = self.ctx._getJavaStorageLevel(storageLevel)
diff --git a/python/pyspark/sql.py b/python/pyspark/sql.py
index e7f573cf6d..97a51b9f8a 100644
--- a/python/pyspark/sql.py
+++ b/python/pyspark/sql.py
@@ -29,6 +29,7 @@ from operator import itemgetter
 
 from pyspark.rdd import RDD, PipelinedRDD
 from pyspark.serializers import BatchedSerializer, PickleSerializer, CloudPickleSerializer
+from pyspark.storagelevel import StorageLevel
 
 from itertools import chain, ifilter, imap
 
@@ -1665,7 +1666,7 @@ class SchemaRDD(RDD):
         self._jschema_rdd.cache()
         return self
 
-    def persist(self, storageLevel):
+    def persist(self, storageLevel=StorageLevel.MEMORY_ONLY_SER):
         self.is_cached = True
         javaStorageLevel = self.ctx._getJavaStorageLevel(storageLevel)
         self._jschema_rdd.persist(javaStorageLevel)