The IOC said 400-meter hurdler Ghfran Almouhamad tested positive for the banned stimulant methylhexaneamine on Aug. 3. Her backup "B'' sample confirmed the positive finding.
The 23-year-old athlete finished eighth and last in her first-round heat on Aug. 5.
The IOC said Almouhamad has been disqualified and stripped of her Olympic accreditation.
The IOC sent her case to the IAAF to officially change the results and consider any further action against the athlete.
Almouhamad was one of 10 Syrian athletes, six men and four women, registered to compete in seven different sports in London. The Syrians came to the Olympics despite the escalating violence in their homeland.
Protests against President Bashar Assad's regime began in March 2011 and became a civil war which activists say has killed at least 20,000 people.
The head of the Syrian Olympic Committee, Gen. Mowaffak Joumaa, was denied a visa to come to London by British authorities.
Almouhamad is the seventh positive case reported by the IOC since the Olympic body started its games testing program on July 16. She is only the second athlete who competed in London that has been sanctioned for doping. The others were caught before competing.
American judo fighter Nick Delpopolo was expelled after testing positive during competition for marijuana, which he said he unintentionally consumed in something he ate.
Gymnast Luiza Galiulina of Uzbekistan and Albanian weightlifter Hysen Pulaku were expelled for failing pre-games tests. Galiulina tested positive for the diuretic furosemide, while Pulaku was caught for using the steroid stanozolol.
Russian track cyclist Victoria Baranova was disqualified after testing positive for testosterone on July 24 in Belarus, and Colombian 400-meter runner Diego Palomeque was suspended for a testosterone positive on July 26 in London.
Italian race walker Alex Schwazer was formally disqualified by the IOC after the Italian Olympic Committee removed him from the team for a positive EPO test in Italy before the games.