Diabetes mellitus (DM) is characterized by oxidative stress, which is one of the major pathophysiological mechanisms underlying diabetic erectile dysfunction (ED). Lycopene is one of the most potent antioxidants among the natural carotenoids. The present study was aimed to investigate whether lycopene could lower oxidative stress and attenuate ED in diabetic rats. Lycopene (10, 30, 60 mg/kg/d) was administered via intragastric intubation for 8 weeks to streptozotocin (STZ) (50 mg/kg, i.v.) induced diabetic rats. The results showed that chronic lycopene treatment significantly and dose dependently restored ED in diabetic rats by lowering blood glucose, reducing oxidative stress and up-regulating eNOS expression. These results indicated that lycopene treatment is potentially a new strategy for treating diabetic ED.