El grupo debutó en 2003 como un grupo de 5 miembros que consistió en el líder U-Know Yunho (유노윤호 ユンホ), Max Changmin (최강창민 チャンミン), Hero Jaejoong (영웅재중 ジェジュン), Micky Yoo Chun (믹키유천 ユチョン) y Xiah Junsu (시아준수 ジュンス).
En julio de 2009 Jaejoong, Yoochun y Junsu presentaron legalmente una demanda judicial en contra de su agencia coreana SM Entertainment.
Sotul este un elev de liceu,jucat de Yoochun,iar sotia e consilier de clasa,jucata de So Hyon Jin.
Ceilalti 4 membrii vor fi colegii de clasa ai lui Yoochun.
Your a great all round actor but I do hope you get a great first lady to be romantic with in a drama or a movie. HAPPY NEW YEAR 2017 (From a fan in Thailand.) I miss u oppa:'(wait for you comeback from millitary! assured that he already got enough rest after coming back, I hope that there'd be a new song and a drama! I feel the sadness with his fans and even himself, but we know you are doing a good job, when duty calls, we are proud of you guys. Two years seems like way too long to have to go without seeing JJ. In November 28, 2012, the legal battle between JYJ and S. JYJ proceeded to release The Beginning, a global album which was sung in English.JYJ promoted the new album via a worldwide showcase tour throughout October and November with dates in South Korea, Southeast Asia and the United States. I think I'm beginning to understand in many songs that you wrote, and it's very good for me to can tell you ; their songs give me truly power. if you are fan of jj u should make sure 2 watch this movie .... HI - my favorite UNIQUE and the best in the world singer (KJJ) WE MISS YOU VERY MUCH AND THINKING OF YOU. I always felt powerful whenever I felt so bad, the song ' love you more' still be youth never change, it's good to next step with those power now, see you soon oppa! If I become a popular singer in Korea I will sign up with sm company and betray them with signing with other company....