In this paper, the performance of a two-way relay (TWR) mixed radio frequency/free space optical (RF/FSO) system with co-channel interference (CCI) is investigated. Different from interference-limited one-way relay (OWR) system, CCIs should be considered at both relay and users in TWR system. Additionally, opportunistic user schedule is applied to select the user with the largest signal to interference plus noise ratio (SINR). Exact and asymptotic outage probability (OP) is derived. Approximate bit error rate (BER) is further presented to evaluate the overall performance. Simulation results show that the performance of a TWR system is dominated by the uplink or downlink whose performance is severer.