Abstract: In this study,the protective effect of water extract from Camellia ptilophylla Chang on the tert-butyl hydroperoxide(tBHP)-induced oxidative damage in mouse fibroblast NIH3T3 cells was investigated. Cell viability was analyzed by methyl thiazolyl tetrazolium(MTT)method and the cell membrane integrity was determined by a lactate dehydrogenase(LDH)kit. Besides,the levels of intracellular reactive oxygen species(ROS),malondialdehyde(MDA),and glutathione(GSH),as well as the activities of catalase(CAT),glutathione peroxidase(GSH-Px)and superoxide dismutase(SOD)were measured to evaluate the antioxidant capacity of Camellia ptilophylla Chang. To further explore the underlying mechanism,the mitochondrial membrane potential(MMP)was detected by a fluorescent probe,and the expressions of caspase-3,caspase-9 and cytochrome c were measured by spectrophotometry and western blot. The results showed that,in comparison with the tBHP group,the water extract of Camellia ptilophylla Chang significantly increased the cell viability of tBHP-induced NIH3T3 from 49.68% to 81.69%. Meanwhile,the LDH activity decreased from 520.70 U/L to 346.42 U/L when the cells were incubated with 25~100 μg/mL of water extract from Camellia ptilophylla Chang. Moreover,the GSH content increased to 3.07 folds while the production of ROS and MDA decreased to 0.02 folds. Furthermore,the increase in the activities of major antioxidase(CAT,GSH-Px and SOD)to 1.42、2.48、1.77 folds respectively,and MMP as well as the inhibition in the expressions of caspase-3,caspase-9 and cytochrome c were observed. These results suggested that the water extract of Camellia ptilophylla Chang could effectively protect NIH3T3 cells from the tBHP-induced oxidative damage by repairing the antioxidant system and inhibiting the mitochondrial apoptotic pathway. The present study preliminarily revealed the antioxidant mechanism of Camellia ptilophylla Chang.It advanced our knowledge of the antioxidant properties of Camellia ptilophylla Chang and provided us with useful information for its further utilization.