Opportunistic routing (OR) has attracted increasing attentions, and several practical protocols over wireless mesh networks (WMNs) have been proposed. Opportunistic routing protocols usually use a fixed rate to send data packet and end-to-end acknowledgement to ensure reliability, which cause congestions and duplicated retransmissions in the networks. In this paper, we propose a built-in rate control mechanism in opportunistic routing to avoid performance degradation due to network congestion. It takes full consideration of the wireless link quality and the non-deterministic multi-path characteristics of opportunistic routing. We also introduce a round-Robin packet sending fashion to reduce unnecessary retransmissions and improve throughput. Simulations show that the modified protocol significantly outperforms the state-of-the-art opportunistic routing protocol, MORE, in both single and multiple flow scenarios.