Exact bit error probabilities (BEP) are derived in closed-form for an impulse radio (IR) multi-access system that employs a single transmit antenna and multiple receive antennas. The transmitted signal passes through a flat Nakagami fading channel and the signals received in multiple antennas are equal-gain combined (EGC) before detection. The characteristic function (CF) method is adopted to develop the BEP, where an exact expression of the CF of multi-access interference is obtained first through a straight forward method. The derived exact BEP expression is simple and good for any arbitrary number of receiving antennas and pulse shape. The theoretical BEP shows absolute match with the BEP obtained from simulations. © 2007 IEEE.