Objective: Aim of the present study is to evaluate the antidiabetic and antihyperlipidemic effect of methanolic extract of Citrullus lanatus seeds (MECL) in streptozotocin (STZ) induced diabetic rats. Methods: Diabetes was induced by a single dose of STZ (65 mg/kg) in citrate buffer, while the normal control group was given the vehicle only. After three days of induction of diabetes, the diabetic animals were treated further four weeks with MECL (200, 400 and 600 mg/kg) and glibenclamide (4 mg/kg). Blood glucose level was estimated every week of the study starting from d 1. At the end of study period, biochemical estimations of blood i.e. lipid profile was performed and animals were sacrificed to carry out liver glycogen estimations. Results: At the end of study period, i.e. 28 d, STZ-induced rats showed marked hyperglycemia, hypertriglyceridemia and hypercholesterolemia. Body weight was reduced and the blood sugar level was significantly elevated in diabetic rats. The four-week treatment with MECL in a concentration of 200, 400 and 600 mg/kg significantly reversed the elevated levels of fasting blood glucose, serum cholesterol, serum triglyceride, liver glycogen, glycosylated haemoglobin with increase in body weight of diabetic rats. Conclusion: Thus the present study suggested the useful potential of Citrullus lanatus seed in diabetes due to its antidiabetic, hypoglycemic and antihyperlipidemic properties.