Some Salvia and Thymus species of Lamiaceae family come into prominence with strong antidiabetic effects. Compared to the other species, there are limited studies on antidiabetic activity of Salvia triloba (ST) and Thymus praecox subsp. skorpilii var. skorpilii (TPS). The aim of this study was to adjust the dosage and to determine the antidiabetic effects of methanol extracts of ST and TPS in streptozotocin/nicotinamide-induced diabetic rats. Type II diabetes mellitus (T2DM) was induced by a single intraperitoneal (i.p.) injection of streptozotocin (STZ) dissolved in 0.1 M cold citrate buffer (pH 4.5) at a dose of 55 mg/kg/body weight (b.w.) and nicotinamide (100 mg/kg/b.w.) was given prior to STZ injection. For adjusting dosage, oral glucose tolerance test (OGTT) was used while insulin tolerance test (ITT), OGTT, blood glucose levels and animal weights were used to evaluate the antidiabetic effects of ST and TPS. According to the OGTT, the most effective doses for ST and TPS were 200 mg/kg and 100 mg/kg, respectively. At the end of three weeks, blood glucose levels of control goup reached to 462.50 mg/dl, whereas ST and TPS-treated groups blood glucose levels decreased less than 200.00 mg/dl. In conclusion, the present study suggests that both of ST and TPS methanolic extracts may be of therapeutic benefit in diabetes and thus need to further studies.