According to the number of successful decoded relay nodes with good destination-to-relay and relay-to-destination link qualities, a simple adaptive relay selection algorithm and its corresponding protocol is presented to achieve a good diversity and multiplexing gains. When the antenna number of the destination is less than the number of successful decoded relay nodes, the opportunistic relay selection scheme is utilized for achieving the diversity gain. Otherwise, the multiplexing selection scheme is adopted to achieve the multiplexing gain. We analyze the outage probability performance, and the asymptotic expression in terms of the outage probability for the proposal is derived. The diversity-multiplexing tradeoff (DMT) and ergodic capacity for the proposed algorithm are also evaluated. Compared with the individual opportunistic relay selection scheme and multiplexing selection scheme, the proposed adaptive relay selection algorithm can provide better capacity and lower outage probability.