diff --git a/graphene/core/types/custom_scalars.py b/graphene/core/types/custom_scalars.py
index bd33df76..c1346c0a 100644
--- a/graphene/core/types/custom_scalars.py
+++ b/graphene/core/types/custom_scalars.py
@@ -16,11 +16,11 @@ class JSONString(Scalar):
     @staticmethod
     def parse_literal(node):
         if isinstance(node, ast.StringValue):
-            return json.dumps(node.value)
+            return json.loads(node.value)
 
     @staticmethod
     def parse_value(value):
-        return json.dumps(value)
+        return json.loads(value)
 
 
 class DateTime(Scalar):
diff --git a/graphene/core/types/tests/test_custom_scalars.py b/graphene/core/types/tests/test_custom_scalars.py
index 28012b36..31cb7855 100644
--- a/graphene/core/types/tests/test_custom_scalars.py
+++ b/graphene/core/types/tests/test_custom_scalars.py
@@ -1,7 +1,7 @@
 import iso8601
 from graphql.language.ast import StringValue
 
-from ..custom_scalars import DateTime
+from ..custom_scalars import DateTime, JSONString
 
 
 def test_date_time():
@@ -24,3 +24,16 @@ def test_date_time():
     node = StringValue(test_iso_string)
     test_dt = DateTime.parse_literal(node)
     check_datetime(test_dt)
+
+
+def test_json_string():
+    test_json_string = '{"foo": "bar"}'
+
+    test_object = JSONString().parse_value(test_json_string)
+    assert test_object == {'foo': 'bar'}
+
+    assert JSONString.serialize(test_object) == test_json_string
+
+    node = StringValue(test_json_string)
+    test_object = JSONString.parse_literal(node)
+    assert test_object == {'foo': 'bar'}