Josefson participated in the World Junior Championship for the second time when he was named for Team Sweden by head coach Pär Mårts for the 2010 World Junior Championships, along with fellow Djurgården teammates Daniel Brodin and Marcus Krüger. He scored his first goal of the tournament and the first goal of the game against Austria in the preliminary rounds. He scored two additional goals in Sweden's 7–1 victory over Finland in the last game of the preliminary rounds. Josefson, who also had three assists in the tournament, had six points in total.