Ben Naceur qualified for the men's 200 m freestyle at the 2004 Summer Olympics in Athens, by clearing a FINA B-standard entry time of 1:54.93 from the All-Africa Games in Abuja one year earlier. He challenged seven other swimmers in heat two, including dual citizen Mihail Alexandrov of Bulgaria. He edged out Singapore's Mark Chay in a close race for fourth seed by a hundredth of a second (0.01), posting his lifetime best of 1:54.69. Ben Naceur failed to advance into the semifinals, as he placed fiftieth overall in the preliminaries.