— This paper investigates the impact of security on the performance of WLAN. More specifically, it analyzes the impact of different implementations of encryption techniques used by two security protocols, namely Wired Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA) on the throughput over WLAN IEEE 802.11g. This paper also addresses the different issues related to the security protocols currently used in WLAN IEEE 802.11g and demonstrates how these issues affect the final results of the experiments conducted. The results show that within the same access point range the security adds moderate degradation on the throughput that may affect some applications over both infrastructure and ad hoc WLANs.