Fading is one of the common characters of a wireless channel. Many rate adaptation mechanisms were proposed to enhance the IEEE 802.11 systems, but these may cause multiple rates in a single network. However, IEEE 802.11 DCF faces the performance anomaly in multi-rate network, that is, when the stations with different rates collide, the low-rate station will greatly degrade the high-rate station. In this paper, we propose a collision avoidance multi-rate MAC (CAMR-MAC) protocol, which is different from the current solutions for performance anomaly. Current performance anomaly solutions are to assign different priorities to stations with different rates based on the IEEE 802.11 DCF protocol, which is still a fully contention based protocol. The simulation results show that CAMR-MAC not only improves the network throughput but also effectively guarantees the temporal fairness of all stations.