Copyright 2019. © by the International Institute of Informatics and Systemics. All rights reserved.The IEEE 802.11p standard defines the specification of Medium Access Control (MAC) and physical layer (PHY) of Vehicle Ad Hoc Networks (VANETs) which uses the Enhanced Distributed Channel Access Function (EDCAF) to support contention-based prioritized Quality of Service (QoS) in the MAC layer. The EDCA (Enhanced Distributed Channel Access) mechanism defines four access categories (ACs). Each AC queue works as an independent DCF station (STA) with Enhanced Distributed Channel Access Function to contend for Transmission Opportunities (TXOP) using its own EDCA parameters. This paper provides an analytical model to compute the performance of the IEEE 802.11p Enhanced Distributed Channel Access Function for Vehicular Network and provides an analytical model to compute the performance of the IEEE 802.11p EDCAF for vehicular network based on packet size. The derived performance model is verified by simulation.