Abstract: In this study, we investigated the protective effects of NaHSO3 on the physiological and biochemical processes of Phaseolus vulgaris leaves under enhanced UV-B radiation. UV-B-induced damage in such leaves could be reduced with 0.5 mmol.L-1 NaHSO3 treatment; brown spots on the leaf surface were reduced in number, the degree of leaf wilt was reduced, degradation of chlorophyll and carotinoid was reduced and flavonoid level was increased. With the NaHSO3 treatment, the content of H2O2 in leaves of Phaseolus vulgaris under enhanc ed UV-B radiation was significantly lower than in controls, and the activities of antioxidant enzymes (POD and APX) were higher with treatment than in controls. The results for chlorophy ll fluores cence parameters (Fv/Fm, ETR) indicated that NaHSO3 treatment could cause increased ability for electron transport in PSII, delay in reduction of maximum efficiency of PSII photochemistry and decreased appearance of the harmful free radicals in chloroplasts. As well, it could also reduce the failure of the photosynthetic mechanism in chloroplasts. Thus,NaHSO3 can effectively reduce the damage to plants induced by enhanced UV-B radiation by improving the enzyme activities of antioxidants (POD and APX) , reducing the production of reactive oxygen species to protect the photosynthetic coloring matter and improving chlorophyll fluorescence parameters.