Choi Jin-sil, 39, whose fame earned her the nickname "The Nation's Actress," is believed to have hanged herself in the bathroom of her Seoul home, said Yang Jae-ho, chief investigator at Seoul's Seocho Police Station.
Family members said she had been depressed since a 2004 divorce and was distraught over rumors linking her to the suicide of a fellow actor a month ago, he said. She had denied the rumors that she had pressed the actor to pay back a large loan.
"It's obviously suicide," Yang told reporters, citing a doctor's examination of Choi's body and testimony from family members and friends. He said an investigation was under way.
An autopsy was planned for later in the day.
No formal suicide note has been found, but Choi sent her makeup assistant cell phone text messages twice Wednesday night asking her to "take care of (my) children no matter what happens" and telling her that "I'm sorry," the investigator said.
Choi's mother told police that the actress returned home drunk around midnight Wednesday, crying and denying the rumor surrounding the other actor's suicide, before going into the bathroom, Yang said.
Choi made her debut in the late 1980s and as a bright-eyed ingenue, quickly becoming one of South Korea's best-loved actresses. She starred in a number of box-office hits, including the films "My Love, My Bride" of 1990 and "How to Top My Wife" of 1994, and TV dramas such as "Jealousy," "My Rosy Life" and last year's "Bad Woman, Good Woman."
The actress was preparing for the second season of the TV drama "The Last Scandal of My Life" in which she played a woman who finds love with a top actor after a painful divorce.
Choi herself had gone through a difficult divorce in recent years. She had married baseball star Cho Sung-min in 2000 while he was playing for the Japanese pro baseball team Yomiuri Giants, but they divorced in 2004, with the deterioration of their relationship becoming tabloid fodder. They had two children younger than 7.
A friend of Choi's told police that the actress had worried about raising the children after the divorce and about her future as an actress and often said she wanted to die, police investigator Yang said.
Her mother also told police that Choi had shown signs of depression after the divorce and had been taking a sedative, Yang said.
Choi had been under stress following the rumors that she had lent money to actor Ahn Jae-hwan, who was found dead in his car last month after committing suicide.
Choi denied the rumors and asked police to investigate who circulated the claims that Ahn killed himself after Choi pressured him to repay the debt.
Yang said a securities firm employee and another suspect are under investigation for defamation.