AIM: To investigate the anti-diabetic effect of a crude ethanolic extract of Andrographis paniculata in normal and streptozotocin ( STZ )-induced diabetic rats.METHODS & RESULTS: Oral administration of the extract at different doses (0.1, 0.2, and 0.4 g/body weight) significantly reduced the fasting serum glucose level in STZ-diabetic rats compared to the vehicle ( distilled water), but not in normal rots. This effect was dose-dependent. A similar result was seen with metfomnin (0.5 g/body weight). In the glucose tolerance test, an oral administration of the extract at the same doses suppressed the elevated glucose level in normal and diabetic rots, as did mefformin. The effects were also dose-respondent. In the long-term experiment, the extract ( 0.4 g/body weight ), mefformin ( 0.5 gz/body weight), and vehicle were given twice daily to diabetic rats for 14 d. On d 15, fasting serum glucose levels were found to be significantly lower in the extract-and mefformin-treated groups ( P＜0.001 ) than in the vehicle-treated group. The mean food and water intakes over 14 days were significantly lower in the extract-treated group ( P ＜ 0.05, P ＜ 0.01, respectively) and also in the mefformin-treated group (both P ＜ 0.001 ) when compared to the vehicle-treated group. No significant change in insulin level was observed among the 3 groups of diabetic rats. The extract, like mefformin, maintained the leptin levels after 14-d treatment, whereas this level was significantly decreased ( P ＜ 0.05) in the vehicle-treated group. The activity of hepatic glucose-6-phosphatase (G-6-Pase) was significantly reduced by the extract as well as by mefformin (both P ＜ 0.05). No significant difference in hepatic glycogen stores was noted among the 3 groups. The extract caused 49.8 % reduction of fasting serum triglyceride levels, compared to 27.7 % with metformin. However, neither the extract nor mefformin significantly affected serum cholesterol level. CONCLUSION: The ethanolic extract of A paniculata possesses antidiabetic property. Its antidiabetic effect may be attributed at least in part to increased glucose metabolism. Its hypotriglyceddemic effect is also beneficial in the diabetic state.