Abstract: Objective To explore effects and potential mechanisms of di-(2-ethylhexyl) phthalate (DEHP) on testes and sex hormones in pubertal male rats.Methods Twenty-four 18-day-old male Sprague-Dawley rats were randomly divided into 4 groups (control,low-,moderate-,and high-dose groups,6 rats in each group) by weight.The rats of dose groups were gavaged with DEHP at doses of 250,500,750 mg/kg/d for 30 days.All rats were sacrificed by decapitation at the end of the treatments.Serum samples were collected and reproductive organs were removed and weighted.Serum testosterone (T),luteinizing hormone (LH),follicle-stimulating hormone (FSH),gonadotropin releasing hormone (GnRH),and 5α-dihydrotestosterone (5α-DHT) levels and testicular glutathione peroxidase (GSH-Px),superoxide dismutase (SOD),malondialdehyde (MDA),and 5α-reductase 2 (5α-R2) levels were measured.Results In the rats exposed to DEHP,the testis index and epididymis index were decreased.Tubular lumina shrinking,structure collapse,breaks of cell membranes,and disordered cell arrangement of seminiferous tubules were observed in the DEHP-treated rats.Levels of T (115.04±14.21 pg/mL) and LH (23.42±3.12 mIU/mL) in the high-dose group were significantly declined compared with those of the control.In moderate-and high-dose groups,FSH levels (5.49±0.42 and 4.63±0.51 IU/L) were significantly lower (P<0.05) than those of the control.Moreover,significantly decreased GSH-Px (728.3±95.3 U/mg pro) and SOD (835.8±151.2 U/mg pro) activities in rat testis were also detected in the high-dose group;on the contrary,MDA level (79.6±13.9 and 90.6±4.0 nmol/mg pro) and 5α-R2 activity (415.9±112.7 and 415.9±147.8 IU/mg pro) in the moderate-and high-dose groups were significantly higher than those of the control (P<0.05 for all).Conclusion After exposure to DEHP,oxidative stress occurred in the testis and serum testosterone level was down-regulated via inducing decreased activity of 5α-reductase 2.