Background and Purpose: Diabetes Mellitus is the most important metabolic disease which can lead to hyperglycemia and hyperlipidemia. Since herbal medicines are rich in natural antioxidants and are associated with few complications, the effect of the hydroalcoholic extract of Ceratonia siliqua L. seeds on the blood glucose and lipids of male diabetic rats were investigated in this study.Methods and Materials: In this experimental study, 56 male mature Wistar rats weighing 210-250 gr were randomly allocated into 7 groups of 8: control group with no treatment, a group daily receiving distilled water, a control group treated with hydroalcoholic extract of Ceratonia siliqua L. seeds (600 mg/kg), a control diabetic group receiving only strptozetocin; and three experimental groups (groups 1, 2, and 3) receiving 600, 300 and 100 mg/kg of oral hydroalcoholic extract of Ceratonia siliqua L.seeds for 16 days respectively, in addition to becoming diabetic by strptozetocin. At the end of experiments, blood samples were prepared from all groups and their blood lipids and sugar were measured. The obtained data were analyzed in SPPS 18 using ANOVA, with P< 0.05 indicating significance.Results: Serum Glucose levels in the experimental groups 1, 2 and 3 were 606±56.75, 582±56.13 and 576±33.01 respectively, which showed a significant reduction in comparison with the control (diabetic) group. Serum total cholesterol levels in the experimental groups 1, 2 and 3 were 57±5.44, 55±6.52 and 61±6.93 respectively, which showed a significant reduction in comparison with the control (diabetic) group (70±5.31). Serum HDL-C level showed a significant increase in the experimental group 2 (24±2.87) in comparison with the control (diabetic) group (22±1.59). Serum triglyceride level significantly reduced in the experimental group 2 (92±8.96) in comparison with the control (diabetic) group (105±9.03).Conclusion: The hydroalcoholic extract of Ceratonia siliqua L.seeds reduced the blood glucose and lipids. HDL-C level increased after the use of this extract.