We assayed the levels of free radical and scavenger in the blood and lens of streptozotocin-in-duced diabetic SD rats, and found that the levels of lipoperoxide(LPO),MDA were higher than that of normal SD rats, and the total superoxygen dismutase (T-SOD), Cu-Zn-SOD) were lower that that of normal rats ( P lt;0.01 ). Simultaneous injection of streptozotocin and large dose of SOD could no avoid the occurence of diabetes mllitus, but did improve the metabolism of free radical in blood and lens. Hence, we think that large dose of SOD might be effective in preventing to development of diabetic cataract which is related to deterioration of free radical metabolism. （Chin J Ocul Fundus Dis,1994,10:25-27）