Garlic (Allium sativum L., Alliaceae), Persian shallot (Allium ascalonicum L., Alliaceae) and Sage (Salvia officinalis L., Lamiaceae) are believed to have hypoglycemic properties and have been used traditionally as antidiabetic herbal medicines in Iran. In this study, diabetes was induced by subcutaneous injection of alloxan monohydrate (100 mg kg-1) to male Wistar rats. Antidiabetic effects of methanolic extracts of the above mentioned three plants on alloxandiabetic rats was investigated in comparison with the effects of antidiabetic drugs such as acarbose, glibenclamide and metformin by measuring postprandial blood glucose (PBG), oral glucose tolerance test (OGTT), inhibition of rat intestinal a-glucosidase enzymes activities and pancreatic Insulin and cardiac Glut-4 mRNAs expression. In short term period, hypoglycemic effects of A. sativum and A. ascalonicum showed significant reduction of PBG similar to glibenclamide (5 mg kg-1 bw) while S. officinalis significantly reduced PBG similar to acarbose (20 mg kg-1 bw). After 3 weeks of treatment by methanolic plant extracts, significant chronic decrease in the PBG was observed similar to metformin (100 mg kg-1 bw). For OGTT, S. officinalis reduced PBG in a similar way as acarbose (20 mg kg-1 bw). Intestinal sucrase and maltase activities were inhibited significantly by A. sativum, A. ascalonicum and S. officinalis. In addition, we observed increased expression of Insulin and Glut-4 genes in diabetic rats treated with these plants extracts. Up regulation of Insulin and Glut-4 genes expression and inhibition of α-glucosidaseactivities are the two mechanisms that play a considerable role in hypoglycemic action of garlic, shallot and sage.