The Belarusian shot-putter who won gold in the Olympics has been stripped of her medal, the International Olympic Committee has confirmed.
Nadezhda Ostapchuk failed a doping test for the anabolic agent metenolone.
It means that Valerie Adams of New Zealand will claim the gold medal and Evganiia Kolodko of Russia takes silver.
China's Gong Lijiao had come in fourth place. She will now get the bronze medal.
The International Olympic Committee (IOC) said Ostapchuk was tested both before and after her event and both of the samples tested positive for the steroid.
The Belarus team had already sent home hammer thrower Ivan Tsikhan because of suspicions over a sample provided after his silver-medal performance at the 2004 Athens Games.
The IOC took almost 6,000 urine and blood samples, including no-notice tests before athletes competed.
The head of the IOC, Jacques Rogge warned that some samples are still being analysed and said: "We might hear something tomorrow or the day after. Hopefully not, but you never know."
Besides Ostapchuk, only one athlete has tested positive for a banned substance after competing.
US judo fighter Nick Delpopolo was cited for traces of marijuana in his urine sample, for which he blamed "inadvertent consumption" of a brownie.
The IOC disqualified him from seventh place in the 73kg class.
"I think that is a sign that the system works," Mr Rogge said. "I am happy about the fact that we could catch athletes who cheated, both before the Games and at the Games."