In the present study, we describe the effects of lycopene on the symptoms of streptozotocin (STZ)-induced diabetes in rats. Lycopene at the dose of 2.5 mg/kg body weight (bw) per day was orally administered to STZ-induced diabetic rats for a period of 7 days after onset of diabetes. At the same time, food-water intake and body weight change were recorded daily. Upon sacrifice, biochemical parameters, such as the serum glucose, insulin, total cholesterol (TC), triglyceride (TG), alanine aminotransferase (ALT), and aspartate aminotransferase (AST), were measured in all experimental groups. Administration of lycopene at the dose of 2.5 mg/kg bw per day significantly reduced serum glucose, TC, TG, ALT, and AST levels, and increased serum insulin levels, but there were no improvements in food-water intake and body weight change parameters in lycopene-treated diabetic rats. The results suggest that orally administrated lycopene exhibits a potent hypoglycemic effect in STZ-induced diabetic rats and that lycopene may be useful for the management of diabetes mellitus.