Abstract Background Capsule fibrosis is the most important and annoying complication of breast implant surgery. Radiotherapy (RT) used in the local treatment of breast cancer has an increasing effect on the existing fibrous capsule; this is called radiation-induced fibrosis (RIF). In this randomized controlled experimental study, we aim to investigate the reduction effect of superoxide dismutase (SOD) on RIF. Methods Sprague–Dawley rats were randomized into four groups, all of which were subjected to implant surgery. No additional procedures were done for the control group. The other groups were the SOD group, the RT + SOD group, and the RT group. The capsules were evaluated histopathologically. Results Although SOD reduced surgery-induced capsule formation, it neither prevented nor reduced significantly RIF. Conclusions In an experimental model that resembled breast cancer treatment, we concluded that SOD cannot reduce RIF but is effective in reducing capsular fibrosis around the silicone after implant surgery. [ABSTRACT FROM AUTHOR]