Effect of cerium (Ce~ 3+) on growth and photosynthesis in rape seedlings exposed to two levels of ultraviolet-B radiation (UV-B, 280～320 nm) was studied with hydroponics under laboratory conditions. The growth of rape seedlings exposed to two levels of UV-B irradiation (0.15 and 0.35 W·m~ -2/T_2) was both heavily restrained. The aboveground growth indices including stem (plant) height, leaf number, leaf area, leaf fresh/dry weight and stem fresh/dry weight were obviously decreased by 13.2%～44.1% (T_1) and 21.4%～49.3% (T_2). Compared to CK, and except active absorption area of roots, the belowground indices main root length, root volume and fresh/dry weight by 14.1%～35.6% (T_1) and 20.3%～42.6% (T_2), respectively. For Ce+UV-B treatments, the aboveground and belowground growth indices were decreased by 4.1%～23.6%, 5.2%～23.3% (Ce+T_1) and 10.8%～28.4%, 7.0%～27.8% (Ce+T_2), lower than those of UV-B treatments mentioned above. These results show that Ce has protective effect on plant against injury of UV-B radiation. Furthermore, the protective effect of Ce on seedlings exposed to T_1 level of UV-B radiation is superior to T_2 level. Chlorophyll content, net photosynthesis rate, transpiration rate, stomatal conductance and water use efficiency in UV-B treatments decrease dramatically, whereas intercellular CO_2 concentration increases. Although these indices in Ce+UV-B treatments decrease compared with those of CK, the decrease in Ce+UV-B treatments are lower than those in UV-B treatment. This phenomenon indicates that the ecophysiological protective effect of Ce is based on improving photosynthesis in plants. The dynamic curves of photosynthesis indices show that the course of light-repair is shortened and the injury to rape seedlings by UV-B radiation stress is alleviated by Ce. The effect of cerium (Ce ~ 3+) on growth and photosynthesis in rape seedlings exposed to two levels of ultraviolet-B radiation (UV-B, 280 ~ 320 nm) was studied with hydroponics under laboratory conditions. The growth of rape seedlings exposed to The aboveground growth indices include stem (plant) height, leaf number, leaf area, leaf fresh / dry weight and stem fresh Compared with CK, and except active absorption area of ​​roots, the belowground indices main root length, root volume and fresh / dry For Ce + UV-B treatments, the aboveground and belowground growth indices were decreased by 4.1% -23.6%, 5.2% -23.3%, respectively, by 14.1% ~ 35.6% (T_1) and 20.3% ~ 42.6% (Ce + T_1) and 10.8% -28.4%, 7.0% -27.8% (Ce + T_2), lower than those of UV-B treatments mentioned above. These results show that Ce has protective effector ct on plant against injury of UV-B radiation. The protective effect of Ce on seedlings exposed to T_1 level of UV-B radiation is superior to T_2 level. Chlorophyll content, net photosynthesis rate, transpiration rate, stomatal conductance and water use efficiency in UV-B treatments decrease dramatically, while intercellular CO 2 concentration increases. Although these indices in Ce + UV-B treatments decreased compared to those of CK, the decrease in Ce + UV-B treatments are lower than those in UV-B treatment . The phenomenon indicates that the ecophysiological protective effect of Ce is based on photosynthesis indices in the course of light-repair is shortened and the injury to rape seedlings by UV-B radiation stress is alleviated by Ce.