The long-term performance of reinforced concrete beams externally strengthened with CFRP composite was evaluated in the present study. The load-carrying capacity and failure mechanism of the beams subjected to different durations in a corrosive environment were examined using four-point bending test. A total of five reinforced concrete beams externally strengthened with CFRP composite were exposed to wet/dry cycles in salt water for 0, 90, 240, and 360 days before tested to failure. The experimental results revealed that the midspan debonding was the dominant mode of failure. The debonding at the CFRP-concrete interface was detected after flexural cracks were developed in the concrete members. The characteristics of the load-deflection curves were relatively similar for all tested beams. The aggressive environment however had the detrimental effects on reducing the bond strength and fracture energy at the CFRP-concrete interface. Additionally, the mode of failure was altered from debonding failure in concrete substrate to failure in the interface epoxy when the beams were exposed to wet/dry cycles. The research findings provided the long-term effectiveness of the CFRP strengthening system in a corrosive environment.