IOC spokesman Mark Adams says Luiza Galiulina has been kicked out of the athletes village after the test confirmed the initial finding for use of the banned diuretic furosemide.
Galiulina—a lesser-known name with no medal hopes—tested positive in a pre-games urine control in London last Wednesday.
She had been provisionally suspended by the IOC pending analysis of the "B" sample.
Galiulina is the second athlete expelled from the games for doping. Albanian weightlifter Hysen Pulaku was disqualified last week after testing positive for the steroid stanozolol on July 23.