The International Olympic Committee said Luiza Galiulina -- a lesser-known name with no medal hopes -- tested positive for the banned diuretic furosemide in a pre-games urine control in London on Wednesday.
After attending a hearing on Saturday night, the 20-year-old athlete was suspended pending the testing of her backup "B sample Sunday afternoon. Galiulina had been due to compete in women's qualifying on Sunday.
On Saturday, the IOC expelled Albanian weightlifter Hysen Pulaku from the games after he tested positive for the banned steroid stanozolol on July 23.
Galiulina won bronze on balance beam at the 2010 Asian Games. This is her second Olympics after finishing 60th in 2008.
She appeared at an IOC hearing Saturday night along with the team coach, her personal coach and two Uzbek officials.
The IOC said Galiulina contended she did not take furosemide and did not know how the substance entered her system. She claimed she had been treated by her mother when she was ill at home last month, had taken medication for a heart condition this month and used "numerous other products and natural herbs" to help her sleep and relax.
The IOC said it found "no corroborating evidence" to support her defense that she had not intended to enhance her performance or mask the use of a banned substance.
The IOC is conducting more than 5,000 urine and blood tests during the Olympics, both in and out of competition. All medalists are being tested.