Software Defined Networking (SDN) is considered one of the major driving factors to bring radical changes on Mobile Core Networks (MCN) design. There are many proposals on how to advocate SDN methodology, however, most of them stop at “vision” level without providing details about key performance contributors. In this paper, we tackle this gap and present a study of latency in SDN based MCN. We identify the major factors and elements in an SDN MCN that contribute to the overall latency. Two types of latency are considered: the processing delay inside the SDN control plane and the transmission delay of SDN control messages between controller and the managed switches. We use a realistic system setup with implementations of SDN controller and SDN application, as well as in-band transfer of control messages among switches and controller. We compare the latency obtained from SDN based MCN with the Evolved Packet Core (EPC). The observed overall latency in our experiments for SDN based MCN is within the EPC requirements. The direct comparison of the SDN versus EPC based MCN in the proposed scenarios show the first can reduce the overall latency. We also identified that the calls to controller APIs can be the major key contributors to the overall latency in SDN MCN, but the act of transmitting more control messages from the controller to the switches to setup longer flowpaths is not a key contributor for the overall latency.