"His body was found at his home in (the southern town) Plovdiv," an interior ministry spokeswoman told Reuters.
"There are no signs of violence on the body, the cause of death is still not clear."
Dobrev won the Olympic title in the 94kg category at the 2004 Games in Athens. He also won gold at the 2003 world championship in Vancouver as well as two European titles.
"I can't stop crying," Bulgaria's former weightlifting coach Plamen Asparuhov said. "He was the best person I ever knew."
Dobrev retired before the 2008 Games in Beijing after failing to recover from a series of injuries.
Bulgarian weightlifters have won 11 Olympic titles since 1972, making it one the most successful sports in the Balkan country.
(Reporting by Angel Krasimirov; editing by Toby Davis)
