Network coding has been proven as a very promising technique to improve wireless network throughput. In multi-rate wireless networks, simply seeking more coding opportunities or encoding more packets into one frame without exploiting multi-rate feature may lead to selecting low-rate links for transmission, and thus compromise the performance gain brought by network coding. In this paper, we aim at exploiting the potential benefits brought by both multi-rate and network coding. We carefully address the bottleneck problem in applying network coding to multi-rate networks, and propose Network Coding with Relay Assistance, called NCRA. We design a Medium Access Control (MAC) protocol based on 802.11 DCF to implement the idea of NCRA. Numerical results of both analytical modeling and simulation experiments based on NS-2 demonstrate that NCRA can significantly improve network performances in terms of both throughput and end-to-end delay, at a relatively low cost of header overhead.