Yesung was born on August 24, 1984 in Seoul and later moved to Cheonan, South Chungcheong at age 10. He is the older son of two; his younger brother's name is Kim Jongjin. From a young age, Yesung expressed an interest in singing. In 1999, he joined a broadcast singing competition and won gold at the Cheonan Singing Competition. In 2001, Yesung's mother signed him up to audition for SM Entertainment's Starlight Casting System, in which he impressed the judges with his "artistic voice", and signed as trainee under SM Entertainment that same year.