Alkali-silica reaction (ASR) causes an increase in concrete volume and results in its failure. The effect of ASR on the strength, ductility and deformability of reinforced concrete (RC) beams under sustained load was investigated in this research. In total, 12 reinforced beam specimens, six with reactive aggregate (R beams) and six with non-reactive aggregate (N beams), were loaded and kept in a suitable environment for 360 d. Flexural loading tests were then carried out and the attributed deflections subsequently analysed with respect to total applied load to check the strength, stiffness, reinforcement yielding load and the ultimate load of the specimens due to ASR. Ductility and deformability analyses were conducted using related parameters. The experimental results indicate that ASR has a considerable effect on the R beams (where cracks occurred at lower loads) and, in the condition of loading up to ultimate load, the N beams were stronger than their equivalent R beams. Likewise, in R beams under load, there was a loss of toughness owing to loss of flexural stiffness. It was also found that, for both compression steel and a higher ratio of tension steel in the beams, the flexural behaviour of R beams and N beams will be quite similar. Furthermore, despite losses in the ductility of most of the R beams, failure of these beams was ductile with sufficient warning.