Network coding has recently received significant attention as an innovative approach to improve the throughput of wireless communication systems. The multiple access relay channel (MARC), in which multiple users communicate with a common destination via relays, is one of the important network coding applications for wireless cooperative communications. In this paper, the effect of co-channel interference in decode-and forward (DF) based MARC model with relay selection is investigated by obtaining the average bit error rate (BER) results of the proposed system for cascaded Rayleigh fading channels. The simulation results obtained by using binary phase shift keying (BPSK) modulation have shown that the proposed system overcome diversity gain reduction due to error propagation, and detrimental effects of the co-channel interference.