To explore the protective effects of L-carnitine on erectile function and reproductive function in rats with diabetes. A total of 60 male diabetes mellitus induced-erectile dysfunction (DMED) rats were randomly divided into three groups, 20 rats in each group. The blank group was fed normally, the control group was fed with 0.9% sodium chloride solution 5 ml/kg/day, and the experimental group was given L-carnitine 300 mg/kg/day. After six weeks, the Corpus cavernosum penis pressure (ICP) and mean arterial pressure (MAP) were measured. The sperm of epididymis were taken to detect the parameters of sperm. After six weeks of treatment, ICP and MAP in the experimental group were significantly higher than those in the control group and blank group (p < 0.05), and sperm density and PR in the experimental group were significantly higher than those in the control group and the blank group (p < 0.05). Superoxide dismutase (SOD) in the experimental group was significantly higher than that in the control group and blank group (p < 0.05). Malondialdehyde (MDA) in the experimental group was significantly lower than that in the control group and blank group (p < 0.05). The follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone in the experimental group were significantly higher than those in the control group and blank group (p < 0.05). We conclude that L-carnitine can significantly improve erectile function and reproductive function in rats with diabetes and it has great potential in the treatment of systemic organ damage in DMED rats.