We investigated anti-diabetic effect of the crude extracts and lectin purified from the leaves of Viscum album collected in Mt. Duk Yu. The induction of diabetes mellitus was confirmed by the presence of statistically significant greater serum glucose levels in strptozotocin-treated rats compared with the untreated non-diabetic group. There are no significant differences in the serum glucose levels compared extracts and purified lectin to tap water in the non-diabetic group after administration through the oral cavity in 29 day. But for streptozotocin-induced diabetic rats the serum glucose level in extracts after administration through the oral cavity was strikely decreased to 36% than tap water in 29 day. Significantly lower glucose level was obtained at 2 hr and 4 hr after administration of purified lectin(0.4 mg/kg) through the peritoneal cavity. These results provide an evidence that Viscum album lectin has an andti-diabetic effect pharmacologically.