Kyu-jong is a member of the sub-group Double S 301.
Kyu-jong enlisted for his mandatory military service on July 23, 2012. He finished his duties on July 22, 2014.
Kyu-jong made played the lead role Crown Prince Lee Shin in his musical debut in "Goong: Musical"
Kyu-jong left DSP Media in 2010 and moved to B2M Entertainment together with fellow SS501 member Young Saeng.