Ack van Rooyen (born January 1, 1930 in The Hague) is a Dutch jazz trumpeter and flugelhornist. He is the brother of Jerry van Rooyen.
Van Rooyen began playing with a military band as a teenager, doing tours of bases in Indonesia. He then studied music at the Royal Conservatory of The Hague, graduating in 1950, then worked with Ernst van 't Hoff and his brother. He played with The Ramblers in 1955-1957, then moved to France in 1957, where he worked with Aime Barelli, Kenny Clarke, Lucky Thompson, and Barney Wilen. In 1960, he relocated to Germany, playing in a big band at Sender Freies Berlin with his brother, in addition to side work with Hans Koller, Bert Kaempfert, and Ake Persson. He settled in Stuttgart in 1967 and worked with musicians such as Volker Kriegel, Charly Antolini, Friedrich Gulda, Slide Hampton, and Eberhard Weber; , he also toured widely during this time.
In 1980 he moved back to the Netherlands, eventually taking a position as an educator at his alma mater, the Royal Conservatory.