The effect of long term administration of cox-2 inhibitor (Rofecoxib) on epididymal sperm characters (male fertility) was investigated in adult male rats by two separate experiments. Rofecoxib was administered orally at two doses 0.35 mg/Kg B.W., and 0.71 mg/Kg B.W. Animals received 0.35mg/Kg B.W. rofecoxib showed a significant increase in weights of head, body of epididymis, percentage of dead sperms and sperm abnormalities with a significant decrease in sperm count in the epididymal head and the percentage of live sperms. On the other hand, rofecoxib at a dose 0.71 mg/Kg B.W. caused a significant decrease in the percentage of live sperms accompanied with a significant increase in the percentage of dead sperms and sperm abnormalities, and the diameter of seminiferous tubules. It is concluded that the administration of rofecoxib was associated with an unexpected incidence of adverse effect on male rat fertility. However, the future might not look quite as satisfying as at first imagined, because it has become apparent that cox-2 inhibitors dose not simply have a significant role in pain and inflammation it might also work disadvantageously.