This paper presents an experimental investigation on the behaviour of reinforced concrete (RC) beams under simultaneous loading and reinforcement corrosion. Corrosion of reinforcements within beams were created by an accelerated method using a 5% NaCl solution combined with a constant impressed current. Three different corrosion durations at 5, 10 and 20 days and four levels of sustained loading at 0, 15%, 30% and 60% of ultimate loading capacity were applied to the beams. Totally 13 RC beams were tested to examine the corrosion of reinforcements, cracking of beams, and structural behaviour of the corroded beams. Test results indicate that corrosion of reinforcements increases with the sustained loading but undergoes an initially increasing rate followed by a decreasing rate. Higher loading level and longer corrosion period are prone to cause the brittle failure of RC beams. Increasing the sustained loading extends the longitudinal crack but not the crack width. The joint effects of sustained loading and corrosion duration, compared to the single effect of either one factor, are more significant on the performance of RC beams in terms of corrosion of reinforcements, failure mode, ultimate loading capacity, and deformation ability. At a higher sustained loading level, beams’ ultimate loading capacity and deformation ability decrease more significantly with the corrosion periods. It is also found that a lower loading increases the flexural stiffness of RC beams, but a higher loading level instead decreases it.