IEEE 802.11 protocol supports adaptive rate mechanism, which selects the transmission rate according to the condition of the wireless channel, to enhance the system performance. Thus, research of multi-rate IEEE 802.11 medium access control (MAC) performance has become one of the hot research topics. In this paper, we study the performance of multi-rate IEEE 802.11 MAC over a Gaussian channel. An accurate analytical model is presented to compute the system saturation throughput. We validate our model in both single-rate and multi-rate networks through various simulations. The results show that our model is accurate and channel error has a significant impact on system performance. In addition, our numerical results show that the performance of single-rate IEEE 802.11 DCF with basic access method is better than that with RTS-CTS mechanism in a high-rate and high-load network and vice versa. In a multi-rate network, the performance of IEEE 802.11 DCF with RTS-CTS mechanism is better than that with basic access method in a congested and error-prone wireless environment. Copyright © 2008 John Wiley & Sons, Ltd.