This paper investigates the co-channel interference effects on sum-rate based relay selection strategy. The investigation considers a dual-hop multiple full-duplex bi-directional wireless relay in the system model. According to analytical, asymptotic and the Monte-Carlo simulation results, sum-rate based relay section strategy outperforms the max-min based strategy. Results also show that the co-channel interference degrades the achievable diversity order from N to 0 and also causes system coding gain losses in high signal-to-noise ratio regimes. On the other hand, the co-channel interference also severely affects the system achievable rate performance and degrades the performance curves at high SNR regimes.