Objective: Pyriproxyfen is a pyridine insecticide and used in agriculture widely. Extensive application of pyriproxyfen to control annual insect pest in agriculture, horticulture and horn garden, leads to environmental pollution and its entrance into the food chain could have determined effects on human and other species. In this research the effects of pyriproxyfen on reproductive parameters of the male rats including serum LH, FSH, testosterone levels, and changes in testicular tissue and body weight were investigated. Methods: For this purpose 250 ? 5g male Wistar strain rats (n = 50) were randomly collected and divided into 5 group of 10, including control, sham (received distilled water 70%+ethanol 20%+aceton 10%as a solvent), and three experimental groups which received 1000, 2000 and 4000 mg/kg/bw pyriproxyfen orally. After 28 days, body and testis weight were measured and blood samples were taken from heart and used for measurement of LH, FSH and testosterone levels. To evaluate histological changes, testes were removed and weighed and, after obtaining tissue section, stained by H and E method. Results: Serum testosterone, FSH, and LH levels showed significant decreasing in experimental groups (p ? 0.05). There was significant decreasing in the number of germinal and somatic cells in testis in experimental groups. There was also a significant decreasing in body and testis weight in experimental groups, as compared to control group. Conclusion: It can be concluded that oral administration of pyriproxyfen could reduction gonadotropins and testosterone hormone levels and also this insecticide might have hazardous effects on testis tissue.