Vehicular Ad hoc NETworks, known as VANETs, are deployed to reduce the risk of road accidents as well as to improve passenger comfort by allowing vehicles to exchange different kinds of data. Medium Access Control protocols play a primary role in providing efficient delivery while minimizing data packet loss. In fact, one of the major challenges of vehicular networks is designing an efficient MAC protocol which can cope with the frequent changes in topology and the different Quality of Service QoS requirements of VANET applications. However, safety applications of VANETs require that vehicles should be able to disseminate messages quickly to their neighboring vehicles with a high degree of reliability and by giving a higher priority to sensitive data to get access to the network. In this paper, we propose a Priority-based Qos Centralized Tdma MAC protocol (PQCTMAC) for vehicular networks in which data priority levels are used to differentiate among slot reservation requests. The main goal of this work is to propose a priority-based scheduling algorithm to make better the use of the single common channel by giving high access priority to safety traffic. Simulation results showed that PQCTMAC significantly improves the efficiency of safety message broadcasting in VANET