Leucaena leucocephala (Lam.) De Wit belongs to the Fabaceae family and is one of the fastest-growing leguminous trees grown throughout tropical and subtropical regions. It has been reported to possess medicinal properties that control stomach diseases, facilitate abortion and provide contraception. It is also a complementary herbal drug in treating diabetes. The study aimed to investigate the anti diabetic activities of Leucaena leucocephala (Lam.) De Wit seed extracts (LLSE), by macerating in 80% ethanol. The antidiabetic activity was carried out by giving a daily dose of 250 mg/kg oral LLSE to normal and streptozotocin (65 mg/kg)-induced diabetic rats for 6 weeks to determine fasting blood glucose level, body weight, serum insulin and blood chemistry in the rats. The results revealed that LLSE showed significant (p<0.05) reduction in fasting blood glucose, blood urea nitrogen (BUN), creatinine, albumin, alkaline phosphatase (ALP), and total protein while significantly increasing serum insulin in the diabetic treated rats compared to the controls. These findings indicated that the seed extracts from L. leucocephala possess antidiabetic activities that lowered the fasting blood glucose level by increasing insulin secretion. LLSE has an effect of reducing fasting blood glucose in diabetic rats with no effects on hematology and the blood chemistry of rats. LLSE can reduce the serum cholesterol and can increase serum insulin in diabetic rats. LLSE does not affect triglyceride LDL and HDL in diabetic rats.