Hyoyeon was born in Incheon, South Korea on September 22, 1989. She is ambidextrous and grew up with her parents and her younger brother Kim Min Gu. She auditioned for SM Entertainment at the age of 11 through SM 2000 Casting System and trained for 6 years and one month. She's the fourth longest SM-trained Girls' Generation member after Jessica (7 years and 6 months), Yoona (7 years and two months) and Seohyun (6 years and 6 months). Hyoyeon herself said she had no intentions to audition. Her mother was a fan of SM Entertainment's boy band H.O.T. and brought her to the SM offices in the hopes, perhaps, of seeing them. For her audition, Hyoyeon danced. In 2004, she was sent to study Mandarin Chinese in Beijing, China alongside with Choi Siwon.