The unprecedented growth in internet applications’ requirement makes adopting smart network architectures such as Software Defined Networking inevitable. Software-Defined Networking (SDN) is a new network architecture that separates the tight coupling between the control plane and the data plane that exists in traditional networks. The purpose of this separation is to enhance the controllability, security, and management of network resources. A controller is the core element of any SDN network, since SDN use as an alternative of traditional networks, different controllers have been developed, such as Beacon, Floodlight, RYU, OpenDay Light, ONOS, NOX, and POX. Due to the diversity of SDN applications and the use of controllers, the choice of the best-fitted controller has become an application-dependent process, therefore, this study evaluates different SDN controllers in trem of their effect on the SDN QoS performance. A comparison between the POX and RYU, which are widely used controllers, was conducted. Mininet and Miniedit was utilized as an emulation tool to compare the performance of POX and RYU controllers. For emulation purpose, Mininet, iperf3, ping, and the tested controllers POX and RYU were ran on the emulation machine that comes with the following specifications; Intel ® Core™ i5-6200 U CPU @ 2.30 GHz × 2 (2 cores) and 4 GB RAM with Ubuntu 14.04 LTS-64-bit operating system. An evaluation for both scenarios, POX and RYU, was conducted to invetiage the performance in term of QoS parameters, namely Throughput, Round-Trip Time, and Jitter using TCP, UDP, and ICMP traffic. The obtained results show that RYU controller performed better compared to POX controller, whereas, the RYU controller recorded 1.24% to 5.35% higher average throughput. In addition, RYU controller obtained 0.5 to 1 ms less delay and around 0.02 ms less jitter values than its counterpart POX controller.