SS301 is a subgroup of the South Korean boy band SS501. It is composed of three SS501 members: Heo Young-saeng, Kim Kyu-jong and Kim Hyung-jun.
Double s 301 made their unofficial debut under DSP Media in 2008 with the EP, "UR Man," as "SS501 Special Project Group" in the absence of SS501 members, Kim Hyun-joong and Park Jung-min.
In 2015, the three members signed under CI Entertainment, who rebranded the group as Double S 301 before releasing their official debut album, Eternal 5, the following year.
Member Hyungjun enlisted for mandatory military service in 2017, temporarily putting the group on hiatus. On December 29, 2018, he was officially discharged from the military, though the group has not returned since 2017.