Abstract: The outage probability of a dual-hop MIMO Amplify-and-Forward (AF) relay network with beamforming technique is investigated, where the source, relay and destination are all equipped with multiple antennas. By supposing that the Maximal-Ratio-Transmission (MRT) and Maximal-Ratio-Combining (MRC) are applied at the transmitter and receiver of each hop, the output Signal-to-Interference-plus-Noise Ratio (SINR) of the dual-hop AF relay system with multiple Co-Channel Interferences (CCIs) and noise at the relay is obtained, and the new closed-form expression of Outage Probability (OP) is derived for the fixed-gain relaying system. The computer simulation results show the effectiveness of the performance analysis; meanwhile, the results are able to provide valuable insights on the effects of key parameters on the performance of the dual-hop AF relaying system, as well as the benefit of implementing multiple antennas.