Rhus verniciflua Stokes(RVS) has been widely used as a food and traditional herbal medicine in Korea. RVS has been reported that the extract from its wood and fruit has strong antioxidant activity and anticancer effect but there is little information on Lacca Sinica Exsiccata(LSE), the resin of RVS, as a medicinal use. The aim of this study was to evaluate the antidiabetic effect of ethanol-eluted extract of LSE on streptozotocin(STZ) - induced diabetic rats. Diabetes was induced in male Sprague-Dawley rats with STZ injection. Oral administration of LSE extract(50mg or 100mg/kg of body weight/day) was given to diabetic group. During 4 weeks of experiment, diabetic rats showed significant weight loss and decreasing feed efficiency ratios(FER) compared with normal rats, while the diabetic group orally fed with LSE extract showed a trend of decreasing weight loss and a significant increase of FER(p<0.05). In 4 weeks after induction of diabetes, diabetic rats showed an increase in weight of liver, kidney and heart, whereas the diabetic rats administered with LSE extract showed a reduction in the weight of heart. Blood glucose level was decreased in diabetic rats treated with LSE extract, but it was not statistically significant. Glutamic oxaloacetic transaminase, Glutamic pyruvate transaminase and total cholesterol levels were lower in the diabetic group treated with LSE extract than in untreated diabetic group, but not significant. These results present that LSE may partly have antidiabetic effect and may protect against the development of diabetic heart complications resulting from impaired glucose metabolism.