SS501 debuted in 2005 with their first single "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 hiatus was due to Heo Young Saeng's throat condition which required 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. 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. On their 600th day (January 28, 2007), they won the Mutizen award from SBS Inki Gayo for their song "Four Chance".
Later in 2007, the group debuted in the Japanese market. A Japanese fanclub has been established with the name of "Triple S Japan"; it officially debuted on March 25, 2007, when SS501 will had first official meeting with the group. In Korea, their fan club members number around 41,700. The group had a Japanese single "Kokoro", which had multiple versions, including one with all members and five others featuring the members individually. The single debuted at #5 on the Oricon chart. 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 6th, 2008, to return to Japanese activities.
On October 2, 2008, an official announcement confirmed Kim Hyun Joong as part of the cast for the Korean version of Hana Yori Dango, also known as Boys Before Flowers, which is scheduled to be broadcast via KBS 2TV in the first half of 2009 with a total of 25 episodes. According to an official from Group Eight, the production house in charge of the drama, Kim Hyun Joong was selected to play Hanazawa Rui, or Yoon Ji Hoo (Korean ver.), because he was deemed suited for the character. The decision was based on his performance in the MBC program ??We Got Married?? where Kim Hyun Joong is being coupled with singer Hwangbo.
Due to two of the members' busy schedules, Jungmin performing in a Korean production of the musical "Grease" and Hyun Joong filming a drama, SS501's album, originally due for release in late 2008, was to be pushed back to July 2009. Instead, a subgroup SS501 was formed. They initially wanted to use Triple S as their group name but gave up the idea because they think that they are 5 members always as 1 no matter what, so they continued to release a special project album U R Man (released on November 25, 2008) under the name of SS501.
The three (members of the subgroup) also had a cameo in the fourth episode of Boys Over Flowers as performers in a club, singing "U R Man". Finishing their promotional activities for 'U R Man', they are currently promoting 'Because I am stupid', a song they sang for the OST of 'Boys Before Flowers'. This song is very well-received due to the success of the drama. They won the "Song of the month (Feb)" award with this song at the 32nd Cyworld Digital Music Awards (28 Mar 09) with about 110,000 downloads for BGM at www.cyworld.com.
The original group, with all five members, is scheduled for a comeback in August 2009. They will have their First Asia Tour from Aug'09, which includes countries like Japan, China, Taiwan, Thailand, etc. Two Asia Tour Concerts has been confirmed, 01 Aug & 02 Aug in Seoul and 13 Aug (1pm & 7pm) in Tokyo. SS501 will hold a fanmeeting in HongKong on 01 Jul prior to their Asia Tour.
They released their official 2nd Japanese album on 13 May 2009 titled "All My Love". They held a 'SS501 ALL MY LOVE Sale Commemoration Hand Shake Session' on 17 May at TFT Hall in Tokyo where 7,000 fans attended.