Little attention has been paid to infertility in men with epilepsy and little information exists about the mechanisms by which anti-epileptic drugs affect spermatogenesis or sperm function. We report a case of a male infertility patient with asthenozoospermia during long-term treatment with anti-epileptic drugs. A 29-year-old man had continued treatment with anti-epileptic drugs under the diagnosis of epilepsy for 13 years. He and his wife had been examined and treated as an infertile couple for 3 years. The patient was found to have no motile sperm with a normal sperm count, while taking a dose of 400 mg/day of carbamazepine. On suspicion of an adverse effect of carbamazepine, he was switched to phenytoin monotherapy. One month after that, sperm motility was vastly improved (65%) and they conceived a child 5 months after that. One must be cautious in extrapolating from a case report, but these findings strongly suggest a direct effect of carbamazepine on spermatic function.