Accepted: 10 June 2019 Software Defined Networks (SDN) differs from traditional networks, it splits the control from the data plane. The controller is an essential and important part in SDN architecture; and it is exposed to many potential security challenges, one of such critical challenges is the impact of Distributed Denial of Service (DDoS) attack. The objective of this study is to implement an Entropy-based detection algorithm for DDoS attacks in SDN networks using POX controller to improve the network security, and to test the performance of this algorithm using POX controller in different topologies and different number of controllers. In this paper the Entropybased detection algorithm was carried out in different tests that include connecting POX controller to single topology with 64 hosts and then different number of POX controller had been connected to linear topology with 64 hosts. Through this study, it was found that the Entropy detection method works better in lightly loaded network and the results indicate that increasing the number of controllers can improve the security of the network. This paper introduces a new contribution in implementing a statistical DDoS detection method in multiple POX controllers and in different topologies to improve the security of the SDN network.