 Nilsson made his Sweden U21 debut on 31 March 2009, in a 2–1 win over Belgium U21, having previously been on the bench in the previous game.Then, Nilsson scored his first goal on 12 August 2009, he scored his first goal for Sweden U21, in a 4–2 win over Denmark U21.In December 2010, Nilsson was called up by Sweden for the first time.