Objective To evaluate effects of cypermethrin on the testis histology and testosterone, LH and FSH in adult male Sprague‐Dawley rats. Methods The intact adult male rats were randomly divided into five groups and were treated with cypermethrin at doses of 0, 7.5, 15, 30, or 60 mg/kg per day by oral gavage for 15‐days. After the treatments, serum was collected for hormone assays. The testes, epididymides, seminal vesicles, and prostates were excised and weighed. The right testis was frozen for daily sperm production and the left one was processed for histopathology. Results Daily sperm production decreased significantly in 30 and 60 mg/(kg day) groups. Testicular structure abnormalities included atrophic and distorted seminiferous tubules, deformed and disordered arrangement of germ cells, reduced germ cells, Sertoli cells and Leydig cells, vacuolization and multinucleated formations of spermatids in the cypermethrin‐treated rats. Vacuolization was found in Sertoli cells and the deformed nucleus was noted in Leydig cells. Serum testosterone reduced significantly in 30 and 60 mg/(kg day) groups. Serum FSH increased significantly in 60 mg/(kg day) group. Conclusion Cypermethrin induces impairments of the seminiferous tubules structure and spermatogenesis in the rats. The damages of the male reproductive system may be attributed to the imbalance of circulating testosterone. Objective To evaluate the effects of cypermethrin on the testis histology and testosterone, LH and FSH in adult male Sprague-Dawley rats. Methods The intact adult male rats were divided divided into five groups and were treated with cypermethrin at doses of 0, 7.5, 15, After the treatments, serum was collected for hormone assays. The testes, epididymides, seminal vesicles, and prostates were excised and weighed. The right testis was frozen for daily sperm production and the left one was processed for histopathology. Results Daily sperm production decreased significantly in 30 and 60 mg / (kg day) groups. Testicular structure abnormalities included atrophic and distorted seminiferous tubules, deformed and disordered arrangement of germ cells, reduced germ cells , Sertoli cells and Leydig cells, vacuolization and multinucleated formations of spermatids in the cypermethrin-treated rats. Vacuolization was found in Sertoli cells and the de Serum testosterone reduced significantly in 30 and 60 mg / (kg day) groups. Serum FSH significantly increased in 60 mg / (kg day) group. Conclusion Cypermethrin induces impairments of the seminiferous tubules structure and spermatogenesis in the rats. The damages of the male reproductive system may be attributed to the imbalance of circulating testosterone.