Marko Ostoja (born 20 October 1960) is a former professional tennis player from Croatia who competed for Yugoslavia.

Ostoja was the Yugoslavian National Champion in 1978, having earlier won the event as a junior, in the 14s, 16 and 18s age groups.

[1] He had his best year on tour in 1981 when he won his first career title at Brussels and reached the doubles finals of the Austrian Open.

[2] He had one of the best wins of his career at the Lipton International Players Championships in Delray Beach that year, defeating world number six Henrik Sundström in straight sets.

He first played Davis Cup tennis for Yugoslavia in 1979 and went on to participate in 11 ties, winning 18 of his 27 matches, 11 in singles and seven in doubles.