We investigate the outage probabil- ity of a dual-hop MIMO system where amplify- and-forward relay and beamforming are used. A practically important case where proportional fair scheduling is implemented to schedule users trans- missions and co-channel interference exists is consid- ered in the analysis. Specifically, taking into account Rayleigh fading and the path-loss effect, we derive the lower bound and the asymptotic expressions of the outage probability in closed form, with arbitrary number of antennas and users. The proposed results are validated via Monte Carlo simulations.