The country's news agency Yonhap wrote that it is suspected that the actor may have committed suicide.
South Korean media reported that the actor was found in the early hours of the day.
Lee Sun-kyun starred in the movie Parasite, which won South Korea the Best Picture Oscar.
Lee Sun-kyun was also reportedly found with a smoking block of coal.
Lee was being investigated on charges of marijuana and psychoactive drug use.
The country's media reported that the actor lost his television and advertising jobs after the drug investigation.
Drug use is investigated as a felony in South Korea.
Lee, 48, reportedly testified for 19 hours over the weekend.
It is also reported that the police found a note in Lee's house.
