Yu Nam-sung

{{short description|South Korean javelin thrower}}

Yu Nam-sung (born 3 October 1978) is a retired South Korean javelin thrower.

He won the 1997 Asian Junior Championships,{{cite web|url=http://www.gbrathletics.com/ic/asj.htm|title=Asian Junior Championships|work=GBR Athletics|publisher=Athletics Weekly|access-date=23 March 2017}} and became South Korean champion once—in 1999—before Park Jae-Myong started a lengthy winning streak.{{cite web|url=http://www.gbrathletics.com/nc/kor.htm|title=South Korean Championships|work=GBR Athletics|publisher=Athletics Weekly|access-date=23 March 2017}} He finished fifth at the 1998 Asian Games and twelfth at the 1999 Summer Universiade.{{citation needed|date=March 2017}} He also competed at the 1999 World Championships without reaching the final.{{World Athletics||name=Nam-Sung Yu}}

His personal best time was 79.84 metres, achieved in April 1998 in Youngju.