The multi-packet reception (MPR) technique enables access points to correctly receive simultaneously transmitted packets. Therefore, the network saturation throughput can be significantly improved by introducing MPR into wireless local area networks (WLANs). In this letter, we develop a novel analytical model to evaluate the saturation throughput of a WLAN with MPR. In contrast to previous models, we adopt the stationary distribution of backoff counter value after a generic overlapping transmission process to characterize the behavior of a contending station. Then, we derive the saturation throughput based on this distribution. Comparisons with simulation results show that our analytical model provides a close evaluation of the saturation throughput. Moreover, the impacts of several parameters on the saturation throughput are also investigated using the proposed model.