2005-2006 : Debut
SS501 debuted on June 8, 2005 with their first single "Kyeonggo" (Korean: "경고", "WARNING"), with a second single "Snow Prince" released in late 2005. The group was inactive in Korea for most of 2006, although they had a fan meeting in Japan in April. The reason was due to Heo Young Saeng's throat condition which required a surgery, thus resulting in a need for time to fully recover.In mid-2006, they held their first concert, "Step Up Concert" in Osaka, Japan. In late 2006, they returned to Korea in order to promote their first full album, which was released on November 10 and titled S.T.01 Now. Singles from the album included "Unlock" and "Four Chance". As well as promoting the album on various variety and music shows, they also filmed a show on MNet called SOS. The group also lent their voices for the 2006 animated movie Pi's Story.
2007-2008 : Japanese activities, 'Boys Over Flower'
Later in 2007, the group debuted in the Japanese market. A Japanese fan club has been established with the name of "Triple S Japan"; it officially debuted on March 25, 2007, when SS501 had their first official meeting with the group. The group released their Japanese single "Kokoro", alongside multiple versions, including one with all members and five others featuring the members individually. The single debuted at #5 on the Oricon chart, and move to #3 the next day. A full album was released later in the year.
In 2008, SS501 returned to Korea with their single Deja Vu released on March 8, 2008. The title track was the first song to be promoted, and they started their comeback on music channel M.Net's M Countdown. After success with their single "Deja Vu", they began to promote their second single, "A Song Calling For You". They performed their Goodbye Stage on Music Bank on June 6, 2008, to return to Japanese activities.
On October 2, 2008, an official announcement confirmed that leader Kim Hyun Joong was part of the cast for the Korean version of Hana Yori Dango, officially named Boys Over Flowers. It was broadcast on KBS in the first half of 2009, with a total of 25 episodes and a few special episodes.
With both Park Jung Min (Danny Park on the musical Grease) and Kim Hyun Joong on solo activities, the next SS501 album was pushed back to July 2009. As such, the other three members released a project album named U R Man in November 2008. The first single released was "U R Man". They also promoted their single for the Boys Over Flowers soundtrack, "Nae Meoriga Nabbaseo" (Korean: "내 머리가 나빠서", "Because I'm Stupid"). Due to the success of the drama, the song had a high number of downloads.
They released their official second Japanese album on May 13, 2009 titled All My Love and had a promotional tour in Japan in support of the album. The group also released their Solo Collection, consisting of the individual members' songs.
On May 22, SS501 was one of many popular groups that performed at the 2010 Dream Concert. And being that Kim Hyun Joong was still recovering from his injuries, they only sang ballad songs.
A day after their performance at the Dream Concert, one of their mini-album tracks, "Love Ya" was leaked on the internet. Not long afterwards, the teaser for the comeback track was released. On May 24, 2010, due to the leaks, DSP Media decided to release SS501's new mini-album, Destination online, which contains six tracks in total. Their first win for their title track "Love Ya" was during their second week of promotion in Music Bank, on June 11, 2010. They also took first place the following week. It was announced from Daesung Entertainment on June 18, 2010 that SS501 will end "Love Ya" promotions due to contract expiry with DSP on June 7, 2010.
On June 28, 2010, It was officially announced that the group's leader, Kim Hyun Joong, signed with a new entertainment(KeyEast Entertainment)Bae Yong-joon's agency to reach his goal as an actor (the entertainment only held actors). Later on, it was rumoured that Park Jung Min also signed with Sony Taiwan, but he clarified that he was still in discussion with the company and thus the 4 of them who has not yet signed with other companies are still under DSP Entertainment.