Glycine max (Soybean) is being used as fresh, fermented or dried food. Petroleum ether (GM-PEE), alcoholic (GM-ALE) and aqueous extract (GM-AQE) of seeds of Glycine max were prepared and evaluated for antihyperglycemic activity. GM-PEE (100 mg/kg), GM-ALE (100 mg/kg, p.o.), GM-AQE (100, 200 and 400 mg/kg, p.o) and glyburide (10 mg/kg, p.o) were administered orally in alloxan-induced(80 mg/kg, i.v.) diabetic mice. Serum glucose level was estimated after acute and chronic treatment with extracts. Oral glucose tolerance test (OGTT) was performed in GM-AQE pretreated animals. GM-PEE (100 mg/kg) and GM-EE (100 mg/kg) did not reduce serum glucose level. GM-AQE (100, 200 and 400 mg/kg) significantly reduced serum glucose level (antihyperglycemic effect) in acute and chronic studies. The antihyperglycemic effect of GM-AQE (100, 200 and 400 mg/kg) showed onset at the 2nd h; peak effect at the 4th h and the antihyperglycemic effect was sustained till the 24th h. In chronic study, reduction in serum glucose level was observed on the 28th day and also after withdrawal for next 7 days. In OGTT, increased glucose tolerance was observed in GM-AQE (100 and 200 mg/kg) treated non-diabetic as well as diabetic mice. It is concluded that GM-AQE but not GM-PEE and GM-ALE showed antihyperglycemic activity.