Reactive oxygen species ate beliceved to play a role in the development of several diseascs incloding vascular disenased and theaging process. It is reported that increased reactive oxygen species were impliated as an important mechanism that contrhibutes to endothelial dysfunciton, So, human umbilical cord vein endothelial cells were used to study the antioxidative effect of L-ascorbic acid and its derivative. The study indicalted that L-ascorbic acid as a tradilonal antioxidant was instable and could protect the cells against hydrogen peroxide induced cytotoxicity as its concetration beiow 50 μg/ml, but hadly could rotect the cells against tert-butyl hydroperoxide induced cytotoxicity, Ascortic acid-2-o-phosphate-6-o-palmitate could effctively protect the cells against hydrogen pcroxide and tert-butyl hydropemoxide induced cytotoxicity, and exhibited no cytotoxicity within the tested concentratin rage. The study indicated that ascorbic acid2-2o2phosphate-6-o-palmite could not only signficantly reduce the intracellular reactive oxygen species level in 3h culture. but also increase the cell viability in 15h culture. In additon. ascorbic acid-2-o-phosphate-6-oi-palmtate could keep stable in RPM1-1640 medium and water for 4 dya. permecat the cell membrane. which in tum may seavenge the intracllular reactive oxygen species. increase the cell viability and the plasminogen activatrs'activity. All above rsults suggested that addition of some hydrophobie groups to the traditonal antioxdants could from novel compounds with better properties.