SANGNYANGHYOLTANG(SYT) is one of the most important prescription that has been used in oriental medicine for diabetes mellitus. The sudy was done in order to elucidate the anti-diabetic effect of SYT. After pretreatment of SYT(1,000mg／kg) for 6 weeks, the effect of of SYT was prevented on serum liver function test and hepatic lipid peroxide content in rats i.v. injected with streptozotocin(STZ, 50mg／kg, tail vein) 5 weeks after pretreatment of SYT. The hepatic microsomal cytochrome P-450 and aniline hydroxylase were significantly decreased, and aminopyrine N-demethylase activity was significantly increased in SYT-STZ group as compared with control group. Changes in aldehyde oxidase, xanthine oxidase, superoxide dismutase, catalase, epoxide hydrolase, UDP-glucuronyltransferase and sulfotransferase activities were not significantly different in any of the group. The cytosolic glutathione S-transferase activity was significantly decreased in SYT-STZ group as compared with control group. The selenium-independent glutathione peroxidase was significantly increased in SYT-STZ group as compared with control group, but there was no significant difference in selenium-dependent glutathione peroxidase in any of the groups. The hepatic glutathione concentration was significantly increased in SYT-STZ group as compared with control group, and ${gamma}-glutamylcystein$ synthetase and glutathione reductase activities were not significantly different in any of the groups. The hepatic lipid peroxide content, serum aminotransferase and sorbitol dehydrogenase activities were slightly decreased in significantly in SYT-STZ groups.