In 2005 Kopitar appeared in three international tournaments for Slovenia; he took part in the U18 Championship, World Juniors, and the senior World Championship, his first tournament with the Slovenian national team. Slovenia competed at the Division I level for both junior tournaments, but at the top level for the senior championship. He would play his last junior tournament in 2006 at the Division I level, with six points in five games. At the 2006 World Championship he played for Slovenia at the top level and recorded three goals and nine points in six games, tying for fifth among scoring leaders. Slovenia was relegated to Division I for 2007, where Kopitar had 13 assists and 14 points, leading the tournament in both categories. Back in the top division for the 2008 IIHF World Championship, Kopitar appeared in five games and had four points to lead his team, though Slovenia was once again relegated.