Later in 2007, the group debuted in the Japanese market to further spread their activities and challenge themselves outside Korea.
The group at this time released their Japanese single Kokoro, alongside multiple versions, including one with all members and five featuring each member individually.
The single debuted at the 5th spot on the Oricon chart, and moved to 3rd spot the next day.
It was also chosen as an ending theme song for an anime entitled Blue Dragon.

SS501 appeared in the Japanese drama Hotelier as a cameo seen in episode seven.
 Later in September, SS501 released their second single in Japan entitled Distance.
Finally in October 24, a month later, a full album was released with their self-titled album, SS501.
SS501 also received the "Newcomer Award" by Japan Gold Disc Award in January 2008; this was the first time for Korean artists to receive this award.

SS501 returned to Korea with their single Deja Vu, which was released on March 13, 2008.
The title track was the first song to be promoted, and they began their comeback on music channel M.Net's M Countdown.
After their 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 in June 2008, to return to Japanese activities.
Their third Japanese single was released on June 18, 2008 entitled Lucky Days.
Then, for a short period of time, they return in Korea and released a mini album entitled, Find.

On October 4, the group represented Korea to perform at the Seoul World Cup Stadium, and received the Best Asian Artist Award at the 5th Asia Song Festival, organised by Korea Foundation for International Culture Exchange.

On October 2, 2008, Kim Hyun-joong was cast for his first lead-acting role as 'Yoon Ji-hoo' in the Korean version of Hana Yori Dango, named Boys Over Flowers, a role for which he won the "Most Popular Actor Award" at the Seoul International Drama Awards 2009 and the "Popularity Award" at the 45th Baeksang Arts Awards.
The series was broadcast on KBS during the first half of 2009.
During this time, around early 2009, Park Jung-min was also cast for his musical debut in Grease as "Danny Park",  where he received the award "Best New Musical Talent" by the Golden Ticket Awards.
While both Kim and Park were busy with their schedules, the remaining three members formed 'SS501 Project Group' with Heo Young-saeng as the leader.
The 'Project Group' was initially to be named after their fan club 'Triple S', however before the sub-unit group debut it was decided to retain 'SS501' name out of respect to the absent members.
They released a project album named U R Man in November 2008, with a high tempo dance track "U R Man", which the three remaining SS501 members promoted by themselves, with the exception of some special performances that included all five band members.
The project group also performed "U R Man" in episode four of Boys Over Flowers, where they appeared for a cameo performance.
Moreover, they contributed to the Boys Over Flowers soundtrack with "내 머리가 나빠서" (Because I'm Stupid) track, in which they received multiple awards such as "Song of the Month (February)", "Best OST Award", and "Best TV Drama Song of the Year" just to name a few.
Later in 2007, the group debuted in the Japanese market to further spread their activities and challenge themselves outside Korea. The group at this time released their Japanese single Kokoro, alongside multiple versions, including one with all members and five featuring each member individually. The single debuted at the 5th spot on the Oricon chart, and moved to 3rd spot the next day. It was also chosen as an ending theme song for an anime entitled Blue Dragon.
SS501 appeared in the Japanese drama Hotelier as a cameo seen in episode seven.  Later in September, SS501 released their second single in Japan entitled Distance. Finally in October 24, a month later, a full album was released with their self-titled album, SS501. SS501 also received the "Newcomer Award" by Japan Gold Disc Award in January 2008; this was the first time for Korean artists to receive this award.
SS501 returned to Korea with their single Deja Vu, which was released on March 13, 2008. The title track was the first song to be promoted, and they began their comeback on music channel M.Net's M Countdown. After their 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 in June 2008, to return to Japanese activities. Their third Japanese single was released on June 18, 2008 entitled Lucky Days. Then, for a short period of time, they return in Korea and released a mini album entitled, Find.
On October 4, the group represented Korea to perform at the Seoul World Cup Stadium, and received the Best Asian Artist Award at the 5th Asia Song Festival, organised by Korea Foundation for International Culture Exchange.
On October 2, 2008, Kim Hyun-joong was cast for his first lead-acting role as 'Yoon Ji-hoo' in the Korean version of Hana Yori Dango, named Boys Over Flowers, a role for which he won the "Most Popular Actor Award" at the Seoul International Drama Awards 2009 and the "Popularity Award" at the 45th Baeksang Arts Awards. The series was broadcast on KBS during the first half of 2009. During this time, around early 2009, Park Jung-min was also cast for his musical debut in Grease as "Danny Park",  where he received the award "Best New Musical Talent" by the Golden Ticket Awards. While both Kim and Park were busy with their schedules, the remaining three members formed 'SS501 Project Group' with Heo Young-saeng as the leader. The 'Project Group' was initially to be named after their fan club 'Triple S', however before the sub-unit group debut it was decided to retain 'SS501' name out of respect to the absent members. They released a project album named U R Man in November 2008, with a high tempo dance track "U R Man", which the three remaining SS501 members promoted by themselves, with the exception of some special performances that included all five band members. The project group also performed "U R Man" in episode four of Boys Over Flowers, where they appeared for a cameo performance. Moreover, they contributed to the Boys Over Flowers soundtrack with "내 머리가 나빠서" (Because I'm Stupid) track, in which they received multiple awards such as "Song of the Month (February)", "Best OST Award", and "Best TV Drama Song of the Year" just to name a few.
SS501