‘Biao 810S’ is a yellow-green mutant of the thermosensitive genic male sterile (TGMS) rice ‘810S’.To elucidate the mechanism of photoprotection in ‘Biao 810S’,we compared the photooxidation characteristics in leaves between ‘Biao 810S’ and ‘810S’ under natural light conditions with treatment of 5 mmol/L methyl viologen(MV).The results showed that the decreasing amounts of the net photosynthetic rate(P_n),maximal photochemical efficiency of PSⅡ in the dark(F_v/F_m),actual photochemical efficiency of PSⅡ in the light(Ф_PSⅡ),photochemical quenching(q_P) in leaves of ‘Biao 810S’ were significantly lower than those of ‘810S’,but the increasing amount of non-photochemical quenching(q_n),activities of PSⅠ and PSⅡ in leaves of ‘Biao 810S’ were significantly higher than those of ‘810S’.The contents of ascorbate(AsA) and glutathione(GSH),the activities of superoxide dismutase(SOD),catalase(CAT),peroxidase(POD),ascorbate peroxidase(APX) and glutathione reductase(GR) in leaves of ‘Biao 810S’ were significantly higher than those of ‘810S’,which led to a less endogenous superoxide anion generation rate(O^-·₂) and malondialdehyde (MDA) accumulation in leaves of ‘Biao 810S’ relative to‘810S’.Under the photo-oxidation treatment,‘Biao 810S’ can maintain higher light system activity and photosynthetic capacity by increasing thermal dissipation,antioxidant content,protect enzyme activities and decreasing accumulations of O^-·₂ and MDA,which showed a stronger tolerance to photoinhibition (photooxidation).