For a scenario of two-way relaying channel where multiple pairs of source nodes wish to exchange information with their partners, the application of existing network coding protocols developed for a single pair of sources can be applicable by using the time sharing approach, and the number of the required time slots increases as the number of pairs. In this paper, we develop a new network coding transmission protocol, which can make all M pairs of source nodes accomplish information exchanging within two time slots. Particularly we focus on a scenario where all nodes are equipped with multiple antennas and the source nodes have less antennas than the relay. Outage probability and diversity-multiplexing tradeoff, which demonstrate that the proposed transmission protocol can achieve a larger multiplexing gain than the time sharing approach, are developed. Simulation results have been also provided to demonstrate the performance of the proposed network coding.