In Brazil, medicinal plants are used according to folk traditions of natives or people who came from African, European or Asian countries. The plants are used in formulations of home remedies such as teas, decoct or tinctures. Objectives:In the present study, we evaluate the effect of Syzygium jambolanum ethanolic crude extract (ECE) in different concentration about serum glucose (GL), triglyceride (TR), cholesterol (CT) since this plant is used in south Brazilian folk medicine to treatment of diabetes mellitus. Methods: Male albino Wistar rats (200 – 250g) were used in the experiment. Overnight fasted animals (normal animals) were divided into two groups (n=6): ECE (125, 250, 500 mg/kg v.o.); control ( vehicle v.o.). Blood was collected by ocular puncture 1, 2 and 3 hours after treatments and GL levels were determined. For oral glucose tolerance test fasted rats were divided into three groups (n=6): hyperglycemic rats (GL 4 g/kg, v.o), ECE (GL plus 125, 250, 500 mg/kg v.o.); control (vehicle v.o.). Blood was collected by ocular puncture 30, 60, 90 and 180 minutes after treatments and GL levels were determined. Diabetes was induced by a single intraperitoneal injection of 200 mg/kg of alloxan monohydrate (dissolved just before use in water). Animals whose development of hyperglycemia (serum GL levels > 300 mg/dL) were allocated into two groups (n=6): ECE (125, 250, 500 mg/kg v.o.); control (C - vehicle v.o.). Blood was collected by ocular puncture 1, 2 and 3 hours after treatments and GL, TR and CT levels were determined. Results: For normal rats, ECE showed significant reduction in the blood glucose levels for 500 mg/kg in 1h (33%; P<0.05). ECE prevented significantly the increase in blood glucose levels after glucose administration for 250 mg/kg in 60 min. (27%; P<0,05) and 90 min. (44%; P<0,001). For diabetic rats ECE showed significant reduction in the blood GL levels for 125 mg/kg in 2h (27%; P<0.001); for 250 mg/kg in 1h (35%; P<0. 01), 2h (45%; P<0,001) and 3 h (45%; P< 0.001). In the same experiment ECE showed significant reduction in the CT for 125mg/kg in 1h (43%; P<0,05), 3h (46%; P<0,05) and 250 mg/kg in 3h (46%; P< 0,001). Conclusion: S. jambolanus´s leaves have beneficial effects on blood glucose and cholesterol levels to diabetics rats. Further pharmacological and biochemical investigations are supposed to elucidate the mechanism of the antidiabetic effect of these leaves.