On February 1, Gugudan released their second single album Act.
4 Cait Sith, with the lead single "The Boots".

On May 17, it was announced that youngest member Hyeyeon would go on a temporary hiatus from all the group activities due to health issues.

Gugudan officially debuted in Japan with a release of their first Japanese single Stand By on September 19.
On September 21, Gugudan held their debut showcase and fanmeeting titled Gugudan 1st Showcase ＆ Fanmeeting "Dear Friend" in Japan at Tokyo Akasaka Blitz.
The group also held their first Japan tour in Osaka and Tokyo starting on December 7, 2018.

Hyeyeon left the group for personal reasons in October 2018.

On November 6, Gugudan released their third EP, Act.
5 New Action, containing six tracks with the lead single "Not That Type".
On February 1, Gugudan released their second single album Act. 4 Cait Sith, with the lead single "The Boots".
On May 17, it was announced that youngest member Hyeyeon would go on a temporary hiatus from all the group activities due to health issues.
Gugudan officially debuted in Japan with a release of their first Japanese single Stand By on September 19. On September 21, Gugudan held their debut showcase and fanmeeting titled Gugudan 1st Showcase ＆ Fanmeeting "Dear Friend" in Japan at Tokyo Akasaka Blitz. The group also held their first Japan tour in Osaka and Tokyo starting on December 7, 2018.
Hyeyeon left the group for personal reasons in October 2018.
On November 6, Gugudan released their third EP, Act. 5 New Action, containing six tracks with the lead single "Not That Type".
Gugudan