This paper investigates the outage performance of dual-hop amplify-and-forward (AF) two-way relaying systems with multiple co-channel interferers at the AF relay and two noisy end-sources. For such, a tight closed-form approximation is derived for the outage probability of the considered systems. In particular, in high SIR regions, with an increasing system SIR, the outage performance does not vary with the number of interferers once the total interference power is given. Simulation results are presented to corroborate the proposed theoretical analysis.