Diabetes mellitus is a most common endocrine disorder, affecting more than 300 million people worldwide. For these therapies developed along the principles of allopathic are often limited in efficacy, Carry the risk of adverse effects, and are often too costly, especially for the developing world. In order to identify complementary or alternative approaches to existing medications, we studied the anti-diabetic potential of leaves of Nigella Sativa. The acute oral toxicity studies of the extracts revealed no toxic effects up to the levels of 2000mg/kg b.wt. The aqueous and alcoholic extracts of 20 and 30mg/kg body weight of Nigella Sativa was screened for the presence of hypoglycemic and antidiabetic activity. In this study diabetes was induced by a single IP dose Alloxan monohydrate in 72hrs fasted rats. The FBGL was carried on 7 th , 14 th and 21 st day and OGTT was measured on 8 th , 15 th and 22 nd day. Glibeclamide was taken as the standard and the results are quite comparable with it. The studies were indicated that the leaves of Nigella Sativa are effective in regeneration of insulin secreting β-cells and thus possess antidiabetic activity. The aqueous and alcoholic extracts showed significant effect in decreasing the Fasting blood Glucose level and oral glucose tolerance test of rats and it’s also showed good hypoglycemic activity in normal glycemic rats. The preliminary phytochemical analysis of the extracts of Nigella Sativa revealed the presence of Alkaloids, Flavonoids, Steroids, Tannins, Anthraquinones, Terpenoids and Cardiac glycoside as the possible biologically active principles. Keywords: Nigella Sativa, Alloxan monohydrate, Glibenclamide, FBGL and OGTT.