Objective:To explore the mechanism by which nonylphenol (NP) interferes with male infertility through evaluation of its effects on epididymal sperm of adult male rats.Methods:Twenty four Sprague-Dawley (SD) rats were used as epididymal sperm donors. Previously rats were administrated with NP (0, 2, 10 and 50 mg/kg) body weight respectively in c oil every forty-eight hours by intraperitoneal injection for 30 days. Computer assisted sperm analysis (CASA) was used to determine parameters of sperm. The sperm morphology examination was conducted with a high resolution microscope.Results:Results indicated that exposure to NP has no effect on body weight, while testes weights were significantly decreased. Computer assisted sperm analysis (CASA) showed significant decline in the percentage of motile spermatozoa (P<0.001), STR and LIN (P<0.01), significant increase in ALH (P<0.001), while significant decline in BCF (P<0.001) respectively. Plasma LDH was significantly increased while; plasmaγ-GT activity was significantly decreased. H2O2production and malondialdehyde (MDA) were significantly increased. The Plasma CAT, GSH-Px and SOD activities were significantly decreased.Conclusions:This concludes that NP leads oxidative stress in the epididymal sperm of rats. Moreover, NP can disrupt sperm motility and alterations in the sperm morphology.