The 25-year-old singer and actress was found dead by her manager on Monday afternoon local time, police told CNN.
“So far, it seems she killed herself, but we will leave all possibilities open and investigate,” a police official said.
Sulli’s manager spoke to her on Sunday evening and went to check on her when he was unable to reach her on Monday.
The singer, whose real name is Choi Jin-ri, was found on the second floor of her house in Sujeong-gu, Seongnam, south of the capital city, Seoul.
Police said they found a note at the scene but have yet to analyze its content. Investigations are ongoing.
Sulli was a child actor before making her singing debut with the girl group f(x) in 2009.
She left the group in 2015 to concentrate on acting before returning to the music scene as a solo artist, releasing a single, “Goblin,” in June 2019.
Sulli also appeared on a TV show in which K-pop stars talked about receiving negative online comments, Reuters reports.
Korean pop music — or K-pop — is one of the country’s biggest exports in the past decade.
Many of its stars — known as idols — train for years, honing their singing, dancing and acting skills, while also learning other Asian languages, before they are even allowed to debut their first song.
Stars of the genre are subject to intense pressure, which has been linked to a mental health crisis in the industry.
K-pop megastar Jonghyun, whose real name was Kim Jong-hyun, ended his own life in Seoul in December 2017.
And singer and actress Goo Hara, formerly part of girl band Kara, apologized to fans after being found unconscious at home in May 2019.
The singer had posted the word “Goodbye,” to her Instagram account, prompting a rush of comments from concerned fans.
Sophie Jeong reported from Seoul and Jack Guy wrote from London. CNN’s Jake Kwon contributed to this story.