The effect of chitin on human umbilical vein endothelial cells (HUVECs) injured by oxygen free radicals was investigated in vitro. The degree of injury was determined by the amount of malondialdehyde (MDA) and lactic dehydrogenase (LDH) in the culture medium. The results indicated that chitin could reduce the amount of MDA and LDH significantly, showing that chitin could protect HUVECs from oxygen free radicals injury.