In this paper, we propose a modified EDCF scheme, M-EDCF, to improve the Quality of Service (QoS) of the IEEE 802.11e wireless network. The IEEE 802.11e standard is presented to support QoS at medium access control level using a priority scheme by differentiating the inter-frame space and the initial window size. In addition to providing relative priorities by adjusting the size of the Contention Window (CW) of each traffic class, our proposed scheme, M-EDCF, also consider the effect of a back_off_timer to avoid unnecessary collisions. Our study shows that in either in heavy or light traffic load our proposed scheme can provide better quality for both high priority and low priority packets than either the AEDCF [L. Romdhani, Ni. Qiang, T. Turletti, Adaptive EDCF: enhanced service differentiation for IEEE 802.11 wireless ad-hoc networks, IEEE Wireless Communications and Networking, Conference. vol. 2, March (2003) pp. 16-20] or the original EDCF.