In traditonnal medicine, several plants were used in diabetes treatment. Among them, the aqueous extract from the leaves of Zizyphus mauritiana Lam (Rhamnaceae) was studied. The extract was administrated per os to Wistar rats made diabetics either temporarily by oral glucose tolerance test (first case) or definetely by subcutaneous injection of alloxan (second case). It was observed a striking decrease of the hyperglycemic arrow (p < 0.05) in the first case, with 300 mg/kg administrated 90 minutes before starting the test. In the second case, the results obtained with a dose of 300 mg/kg once or twice a day were identical as those with glibenclamide at 0.2 mg/kg per day. So, the antidiabetic activity of Zizyphus mauritiana Lam was experimentally born out but it has to be standardized for common use.