The International Olympic Committee has confirmed that 454 doping samples from the Beijing Olympics in 2008 have been retested, 31 of which have flashed up as positive.
The repeated tests focused heavily on athletes that could potentially feature at this year's Games in Rio de Janeiro.
No names have been mentioned yet, but those that have been caught will be banned from competing in Brazil.
"All these measures are a powerful strike against the cheats we do not allow to win. They show once again that dopers have no place to hide," said IOC president Thomas Bach.
A further 250 samples from London 2012 have also been retested, with the results to be announced in the near future.
