OBJECTIVE: To investigate the protective effect of curcumin extracted from Jianghuang(Rhizoma Curcumae Longae) against ultraviolet B(UVB) and the possible mechanism.METHODS: Effects of curcumin were detected in vivo and in vitro. Morphological changes of white guinea pig skin were assessed by hematoxylin and eosin staining. Ha CaT cell proliferation was measured by 3-[4,5-dimethylthylthiazol-2-yl]-2,5 diphenyltetrazolium broide(MTT) assays. The cell cycle distribution, apoptotic rate, level of reactive oxygen species(ROS), mitochondrial membrane potential, and intracellullar calcium ion concentration of Ha CaT cells were detected by flow cytometry. Antioxidant levels in skin tissues and Ha Cat cells were measured by biochemical methods.RESULTS: UVB inhibited in vitro cell proliferation by inducing G2/M arrest, increasing ROS, apoptosis,and necrosis, and decreasing B-cell lymphoma-2,and increasing Bax, cytochrome c, and caspase-3 levels.CONCLUSION: Curcumin blocks the effects of UVB by reducing ROS and apoptosis, and reversing UVB-induced changes in the expression of apoptotic proteins. The mitochondrial pathway is involved in curcumin-regulated apoptosis.