Mark Chay Jung Jun (simplified Chinese: 蔡荣俊; born 18 February 1982) is a Singaporean freestyle swimmer who has represented the Republic in, amongst others, the SEA Games and Summer Olympics. His international swimming career began at the 1997 SEA Games, and stretched all the way till the 2005 SEA Games. In between, he has competed in a total of five SEA Games, two Asian Games, two Commonwealth Games and two Olympics.