diff --git a/arango/api.py b/arango/api.py
index 46d8ed32..251de2e3 100644
--- a/arango/api.py
+++ b/arango/api.py
@@ -35,7 +35,7 @@ def __init__(self, protocol="http", host="localhost", port=8529,
         self.password = password
         self.db_name = db_name
         # self.client = SessionArangoClient() if client is None else client
-        self.client = DefaultArangoClient() if client is None else client
+        self.client = SessionArangoClient() if client is None else client
 
     @property
     def url_prefix(self):
diff --git a/arango/database.py b/arango/database.py
index ae005291..02256ed1 100644
--- a/arango/database.py
+++ b/arango/database.py
@@ -404,10 +404,9 @@ def remove_aql_function(self, name, group=None):
     # Transactions #
     ################
 
-    # TODO deal with optional attribute "params"
     def execute_transaction(self, action, read_collections=None,
-                            write_collections=None, wait_for_sync=False,
-                            lock_timeout=None):
+                            write_collections=None, params=None,
+                            wait_for_sync=False, lock_timeout=None):
         """Execute the transaction and return the result.
 
         Setting the ``lock_timeout`` to 0 will make ArangoDB not time out
@@ -419,6 +418,8 @@ def execute_transaction(self, action, read_collections=None,
         :type read_collections: str or list or None
         :param write_collections: the collections written to
         :type write_collections: str or list or None
+        :param params: Parameters for the function in action
+        :type params: list or dict or None
         :param wait_for_sync: wait for the transaction to sync to disk
         :type wait_for_sync: bool
         :param lock_timeout: timeout for waiting on collection locks
@@ -433,11 +434,13 @@ def execute_transaction(self, action, read_collections=None,
             data["collections"]["read"] = read_collections
         if write_collections is not None:
             data["collections"]["write"] = write_collections
-        params = {
+        if params is not None:
+            data["params"] = params
+        http_params = {
             "waitForSync": wait_for_sync,
             "lockTimeout": lock_timeout,
         }
-        res = self._api.post(path=path, data=data, params=params)
+        res = self._api.post(path=path, data=data, params=http_params)
         if res.status_code != 200:
             raise TransactionExecuteError(res)
         return res.obj["result"]
diff --git a/arango/tests/test_transaction.py b/arango/tests/test_transaction.py
index 70c0c407..c132a24e 100644
--- a/arango/tests/test_transaction.py
+++ b/arango/tests/test_transaction.py
@@ -44,5 +44,33 @@ def test_execute_transaction(self):
         self.assertIn("doc02", self.col02)
 
 
+    def test_execute_transaction_params(self):
+        action = """
+            function (params) {
+                var db = require('internal').db;
+                db.%s.save({ _key: 'doc11', val: params.val1 });
+                db.%s.save({ _key: 'doc12', val: params.val2 });
+                return 'success!';
+            }
+        """ % (self.col_name01, self.col_name02)
+
+        params = {"val1": 1, "val2": 2}
+
+        res = self.db.execute_transaction(
+            action=action,
+            read_collections=[self.col_name01, self.col_name02],
+            write_collections=[self.col_name01, self.col_name02],
+            params=params,
+            wait_for_sync=True,
+            lock_timeout=10000
+        )
+
+        self.assertEqual(res, "success!")
+        self.assertIn("doc11", self.col01)
+        self.assertIn("doc12", self.col02)
+        self.assertEqual(self.col01["doc11"]["val"], params["val1"])
+        self.assertEqual(self.col02["doc12"]["val"], params["val2"])
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/setup.py b/setup.py
index 84b4e372..3d836fc5 100644
--- a/setup.py
+++ b/setup.py
@@ -7,7 +7,7 @@
 setup(
     name="py-arango",
     description="Python Driver for ArangoDB",
-    version="1.3.0",
+    version="1.4.0",
     author="Joohwan Oh",
     author_email="joowani88@gmail.com",
     url="https://github.com/Joowani/py-arango",