Dr. Mani Jegathesan, chairman of the Olympic Council of Asia's medical committee, said Muminov's urine sample showed traces of the banned stimulant Methylhexaneamine.
The 27-year-old Muminov lost the gold medal match in the 81-kilogram division to South Korea's Kim Jae-bum on Sunday night.
Muminov "has been disqualified from the competition as well as these games and his performance has been nullified, his medal withdrawn and appropriate adjustment made to the results," Jegathesan said. "We have had discussions with the athlete on the possibilities of where he got the substance."
Jegathesan said the substance did not come from the athletes' village, where organizers have been providing food, drink and medicine to athletes.
The findings have been referred to the Uzbekistan committee, the international judo federation and to the World Anti-Doping Agency, which will determine any further sanctions after holding a hearing with Muminov, he said.
WADA recently loosened the classification of Methylhexaneamine for next year to the "specified stimulant" list, which covers drugs that are more susceptible to inadvertent use and can carry reduced penalties.
Sanctions for use of the drug can be reduced if athletes prove they did not intend to enhance performance. Penalties range from a warning to a two-year ban.
The Uzbekistan delegation declined comment when reached by telephone by The Associated Press.
Muminov won a bronze medal in the 73-kilogram class in the Asian Games at Doha four years ago.
At the 2008 Beijing Olympics, Muminov lost in the round of 16 but advanced to the second round of the repechage round before losing to eventual bronze medalist Leandro Guilheiro of Brazil.Competition began at the Guangzhou Games last Saturday and continues through November 27. There are more than 10,000 athletes competing in 42 sports. Judo was contested over the first four days.
Asian Games organizers have said all of the anticipated 1,500 urine and 200 blood tests taken during the games will be assessed at the WADA-accredited lab in Beijing, which did drug screenings during the 2008 Olympics.
About half of the tests have been carried out so far, including 700 urine tests and 50 blood tests, Jegathesan said. Among those, 150 were conducted before the competition began.
Chinese anti-doping authorities took measures to avoid embarrassment in Guangzhou by conducting 1,950 pre-games tests on all their athletes eligible for selection.
Every one of the almost 1,000 athletes in China's Asian Games team has been tested at least once in the pre-competition phase, Chinese Olympic Committee officials have said.
At the last Asian Games at Doha, Qatar in 2006, four weightlifters tested positive to banned substances, including a silver medalist from Myanmar in the 75-kilogram category and an Uzbek lifter who tested positive for cannabis.
Iraq's Saad Faeaz, a bodybuilder, was disqualified from the Games after a banned steroid was found in his luggage in Doha International Airport.
Two other bodybuilders flunked tests in cases that were announced after the games.