Di-n-butyl phthalate (DBP) is a ubiquitous environmental pollutant, extensively used as a plasticizer in many products including plastics, cosmetics and medical devices. Previous studies have shown that DBP has potential testicular toxicity. Epididymis is known to play an important role in the maturation and storage of sperm. However, the effect and mechanism of action of DBP on epididymis is unclear. The present study was designed to investigate the effect of DBP on structure and function of epididymis in adult male rats by histological and biochemical study. Oxidative stress was also assessed in rat epididymis as an underlying mechanism. Forty SD adult rats were randomly allotted to four groups, and DBP was administered to each group by oral gavage at doses of 0 (control), 100, 250 and 500 mg/kg/day for 2 consecutive weeks. The results indicated that the epididymal toxicity of DBP is dose-dependent. Epididymal weight, activities of epididymal alpha-glucosidase and glutathione peroxidase (GSH-Px) was significantly decreased in rats of 500 mg/kg DBP exposure group compared to the control. The activity of superoxide dismutase (SOD) was significantly decreased while the level of malondialdehyde (MDA) was significantly increased in the epididymal tissue of the 250 and 500 mg/kg DBP exposure groups compared with the control group. Moreover, microscopy with hematoxylin and eosin (HE) staining showed that atrophy of epididymal tubules, the interstitial vascular was hyperemia and the lumina were oligozoospermic in rats of 500 mg/kg DBP exposure group. In conclusion, DBP exposure alters the epididymal structure and function by inducing oxidative stress in epididymis of adult rats.