BACKGROUND: Diabetes mellitus (DM), as a metabolic disease, has a high rate of mortality all over the world. In recent years, there is accumulating evidence that show this complex multifactorial disease has various effects on reproductive system. OBJECTIVES: This study aimed to investigate the effect of hydroalcoholic extract of parsley (Petroselinum cris-pum) leaves on spermatogenesis and pituitary-gonadal axis in male streptozotocin (STZ)-induced diabetic rats. METHODS: In the present study, 60 male rats were divided into 5 groups of 12 animals in each: control, DM control and 3 experimental groups (treated with doses 1, 2, and 4 gr/kg of hydroalcoholic extract of parsley leaves gavage for 28 days). DM was induced 48 h after intraperitoneal injection of a single dose of STZ (65 mg/kg). At the end of the treatment, rats were bled from the heart and follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone levels were measured. The testes of rats were isolated and weighed. Assessment of the sperm motility and evaluation of the seminiferous cells were performed using light microscopy. RESULTS: Comparison of LH, FSH and testosterone in rats treated with doses 1 mg/kg of hydroalcoholic extract of the plant revealed a significant increase as compared to the diabetic control group (P≤0.05). In addition, the results of histopathological evaluation elucidated a significant increase in the sperm cells number, and motility, testis weight, and total sperm count. It also improved condition of the seminiferous cells in the experimental group (1 mg/kg) compared to the diabetic control group (P≤0.001). CONCLUSIONS: It seems that parsley (P. crispum) hydroalcoholic extract can be effective in decreasing repro-ductive disorders in DM patients.