Dembélé made his first international appearance on 20 May 2006 against Slovakia, coming on as a substitute for Luigi Pieroni. He scored his first international goal in October 2006 against Azerbaijan. Dembélé participated in the 2008 Summer Olympics, where he put on a remarkable show, being instrumental in Belgium's 3–2 win to Italy in the quarter-finals, scoring two goals, including the defining goal of the match. Belgium then progressed, losing to Nigeria in the semi-finals and Brazil in the third place play-offs. Dembélé played in all six of Belgium's games at the Olympics.