2, 2', 4, 4', 5-pentabromodiphenyl ether (BDE-99) is one of the most persistent congener and is considered as an endocrine-disruptor. In utero exposure causes permanent effects on male reproductive system in adulthood but there is a lack of information regarding the effects on male reproduction in adults. Moreover, the mechanism through which BDE-99 causes reproductive effects is not well elucidated. The aim of this study was to evaluate the effects on rat male reproductive system. Adult male rats (10/group) received BDE-99 by gavage at single dose of 0, 0.6 or 1.2 mg/kg/body weight. Forty-five days after the exposure, several fertility parameters as well as oxidative stress parameters in testes and epididymus were evaluated. No changes were seen in testicular or epididymal weights. The exposure to BDE-99 caused impaired spermatogenesis by the means of reduced spermatogenesis and spermatid counts. Histopathological examination of the testes revealed tubular atrophy in all exposed groups. In rat testes, BDE-99 exposure induced a significant increase in thiobarbituric acid-reactive substances (TBARS) at the highest dose. In epididymus, SOD activity was significantly reduced by BDE-99 exposure at both doses. The results of this study suggest that BDE-99 exposure causes oxidative damage in male reproductive system and this could be a mechanism of BDE-99 induced toxicity.