IEEE 802.11 has become the standard of medium access control (MAC) in wireless ad hoc networks. However, due to the embedded binary exponential backoff algorithm, the packet delay and jitter incurred by access collisions and frame retransmissions may grow drastically. The lack of time-constraint considerations in IEEE 802.11 makes it very difficult to provide QoS (Quality of Service) guarantees for multimedia services. Therefore, a lot of research works focusing on priority-based MAC protocols for wireless ad hoc networks have been proposed. Yet, no standards come out until now. This thesis presents a priority-based MAC scheme in wireless ad hoc networks, which not only provides differentiated services, but also improves the QoS limitations of the previously proposed schemes. The main idea of the proposed JMAC (jamming-based MAC) mechanism is that traffic flows with different priorities can be differentiated by transmitting jamming noises of different lengths to interfere with one another. The one with the longest length of jamming noise can start data transmission. Besides, in our design, priority can be dynamically adjusted to allow each MH to change its contention priority and the length of jamming noise in accordance with network congestions. To implement the proposed JMAC, three modules are developed in this thesis: Collision Avoidance, Starvation Prevention, and Deadlock Prevention. For the purpose of evaluation, we perform simulations on the well-known network simulator, NS-2. Our scheme is compared with the EDCF (enhanced distributed coordination function) of IEEE 802.11e¡]draft¡^and one of the existing works. The simulation results demonstrate the effectiveness and superiority of our scheme.