With the Dutch national team, Keizer played 34 times, scoring 11 goals. He made his international debut in an 8-0 friendly win against the Netherlands Antilles in 1962. Keizer was selected by Netherlands manager, Rinus Michels, to play for the Dutch squad during the 1974 FIFA World Cup, but only started in the 0-0 draw against Sweden. He wasn't used for the rest of the tournament and the World Cup final against Germany.