The International Olympic Committee (IOC) says 23 competitors at the London 2012 Games have failed retrospective doping tests.
Those athletes are from six different countries and five sports, the IOC said on May 27.
The IOC retested 454 selected doping samples from the 2008 Games in Beijing and a further 265 from London 2012, using "the very latest scientific analysis methods."
"We want to keep the dopers away from the Olympic Games in Rio de Janeiro" in August, said IOC President Thomas Bach.
The organization announced last week that 31 athletes from the Beijing Games tested positive following reexamination of their samples.
Russia confirmed that 14 of them were Russian athletes and included some medalists.
The Russian government has announced plans to pass legislation making it a criminal offense to use illegal drugs to boost performance in sports.