Lee Sang Yeon is the leader, main vocalist and dancer of IST Entertainment’s boy group The Boyz. Debuted on December 6, 2017 with the lead single "Boy" from their debut EP "The First". Lee is a former MBK Entertainment trainee. Sang Yeon was known for appearing in various music video such as Ailee’s If you and Melody Day’s You Seem Busy.
On March 20, 2020, it was announced that The Boyz will join Mnet’s reality television competition "Road to Kingdom" and reached 1st place during the final episode. The Boyz also participated in "Kingdom: Legendary War" in 2021, where the group finished in 2nd place.
Lee has been selected as Brand Ambassador, Muse and Model for various brands such as SIERO Cosmetics, Lapothicell, Skoolooks School Uniform, Hang Ten, What It IsNt, Olatte and Nongshim Kalgugsu. He’s also selected as Goodwill Ambassador for "Save the Children" campaign and participated in "#END Violence" campaign.