Mladen Košćak (also spelled Koščak; 16 October 1936 – 3 August 1997) was a Croatian and Yugoslav footballer.

Košćak soon established himself as a first-team regular and was instrumental in Dinamo's 1957–58 Yugoslav First League title.

Although he was considered a huge talent, his career was hampered by a serious injury and he effectively stopped playing by 1960, appearing in only a single match in his last three years with the club before retiring in 1963.

[1] Internationally, he was capped 4 times for the Yugoslavia national football team and was member of the national squad which won the silver medal at the 1956 Summer Olympics in Melbourne.

[4] This biographical article related to a football defender from Croatia is a stub.