Adrianus Johannes Steylen (born 1 August 1935) is a Dutch former long-distance runner. He is a five times Dutch marathon champion, who enhanced the Dutch record five times. He was also a four-time winner of the 25-kilometre race and a one-time champion of the 800 metres distance at the Dutch Championships. In 1968, he represented his country in the 1968 Summer Olympics in Mexico. In the 1970s he worked as national coach for the (KNAU). Steylen participated in the Berlin Marathon of 2003 at age 68, finishing in only three hours and 15 minutes. Steylen is a vegetarian.