- 안돼, 난 안돼 (No way)
- Obsessed prod. by Brian Kennedy & Chief Wakil
- Obsessed by Hillary Lindsey prod. by Brian Kennedy
- Oh Holy Night by TVXQ! (동방신기) prod. by 이수만 (Lee Soo Man)
- One Dream (Ft. Henry Lau & KEY (SHINee)) prod. by Toby Gad
- ONE SHOT, TWO SHOT prod. by GRADES
- 세상의 어디에서도 (One Way)
- 완전한 날개 (One Wings-Embracing Each Other)
- 사랑 하나죠 (Only Love) by SMTOWN prod. by 이재명 (Lee Jae Myung) & 이수만 (Lee Soo Man)
- Only One prod. by 김용신 (Kim Yong Shin) & 김태성 (Tesung Kim)
- Only One by Gallant prod. by Darion Ja'Von Dean & lophiile
- Only One by Soulmate (소울메이트) (Queendom Puzzle)
- Only One (Instrumental)
- Only One (Japanese Ver.) prod. by 土屋望 (Nozomi Tsuchiya)
- 하루하루 (Ordinary Day) prod. by 이수만 (Lee Soo Man)
- OUR LOVE〜to my parents〜
- OUTGROW〜Ready butterfly〜
- Outlaw by GOT the beat prod. by Heffybeluga & Ronny Svendsen
- OVER~across the time~ prod. by tearbridge production