TS娛樂
In 2008, a TS Entertainment agent had seen Hyoseong in "Diary of Five Girls" and contacted her to audition for their company. Hyoseong passed the audition and began living as a TS Entertainment trainee. TS Entertainment announced that they would debut a four-member girl group in October 2009. Hyoseong, along with Han Sunhwa, Song Jieun and Jung Hana, debuted as the group, Secret. Prior to their debut, the group appeared in a documentary called "Secret Story" which chronicled their debut process. They released their debut single "I Want You Back" in October 2009.