Multimedia application such as Voice over IP (VoIP) and Video Conferencing are the two demanding applications in the recent times. These applications are noise and delay sensitive due to their variable bit rate characteristic and require higher bandwidth. Therefore quality of service (QoS) has become essential consideration for supporting such applications. The Worldwide Interoperability for Microwave Access (WiMAX) is a popular wireless broadband technology having strong provision for QoS support of multimedia applications. This publication investigates the performance of VoIP and Video Conferencing over WiMAX network. Parameters that indicate Quality of Service such as delay, jitter, packet loss and throughput are analysed construction different scenarios on the basis of different service flows and codecs defined in WiMAX system. OPNET Modeller 14.5 has been used to design and simulate VoIP and Video Conferencing scenarios for the WiMAX Network to analyze its performance capabilities over these real time multimedia applications. The result suggests that better QoS is achieved by using appropriate service flows designed for specific applications.