The Ukrainian four-woman rowing team was stripped of its bronze medal on Thursday after one member tested positive for a banned drug, the IOC said.
It was the fourth medal lost because of doping during the Athens Olympics.
A weightlifter from Hungary was also expelled from the games on Thursday for failing to provide a urine sample after his event, the International Olympic Committee said.
Zoltan Kovacs, who finished last in the 105-kilogram class, became the 10th weightlifter punished for doping.
Three medals have been stripped in the last four days because of doping violations. Hungary's Robert Fazekas lost his gold in the discus and Russian Irina Korzhanenko lost her gold medal in shot put.
Olena Olefirenko was part of Ukraine's four-woman crew that finished third in lightweight sculls on Sunday. Australia finished fourth and will now get the bronze. Germany won the gold and Britain took the silver.
Olefirenko was given Instenon, which contained the banned substance ethamivan, by her team doctor, the IOC said. Olefirenko said that she took the drug when she was tested after the race, but didn't realize it was banned.
"She had listed the product believing in good faith it was something permitted and there was no way she could be aware it contained a prohibited substance," said Denis Oswald, president of the International Rowing Federation and an IOC executive board member.
{{/usCountry}}"She had listed the product believing in good faith it was something permitted and there was no way she could be aware it contained a prohibited substance," said Denis Oswald, president of the International Rowing Federation and an IOC executive board member.
{{/usCountry}}If one member of a rowing crew fails a drug test, the entire crew loses the medal.
"Because of a mistake of a doctor, four innocent athletes lose their medal," Oswald said.
He said the rowing federation would probably not take any action against the rower, but has been asked by the IOC to consider sanctions against the doctor, Ganna Gryshchenko.