Abstract: In order to investigate the relationships between CMS and metabolism of reactive oxygen species, anthers and leaves of cytoplasmic male-sterile rice and its maintainer at reproductive stages were used as experimental materials to measure the production rate of O₂^-, contents of H₂O₂ and MDA, and activities of antioxidant enzymes (SOD, CAT and POD). The results showed that at reproductive stages, anthers of CMS line had higher production rate of O₂^-, contents of H₂O₂ and MDA, in comparison with the maintainer line. The activities of SOD and CAT were obsessively lower in CMS anthers, whereas POD activity of CMS anthers was higher than those of maintainer line. There were only differences in contents of H₂O₂ and MDA, and activity of CAT in leaves of male-sterile line and maintainer line. Based on the above results, the differences of the reactive oxygen metabolism between CMS and its maintainer were mainly apparent in anthers. In the process of anthers development, disordered metabolism of O₂^- and H₂O₂, excessive accumulation of MDA and decline of protective enzymes activities or function change of some protective enzymes may be the important reasons to make male sterility.