The Miss Universe Organization said it fired the 24-year-old law student Monday the first time in the pageant's 52-year history that it has ousted a woman wearing the crown.
The first runner-up, Miss Panama Justine Pasek, 22, was to be crowned Tuesday.
Paula Shugart, president of the Miss Universe Organization, said Fedorova was dethroned because she "was unable to fulfill her duties," chiefly traveling around the world for charities.
"She needed to spend a lot of time in Russia," Shugart said in a broadcast interview. "I believe her mother was ill at one point."
When asked about reports that Fedorova was fired because she was married or pregnant, Shugart said, "No, I honestly have no idea where any of that came from." Miss Universe cannot be married or have children, according to pageant rules.
Fedorova, a police lieutenant pursuing a graduate law degree at St. Petersburg's Police Academy, denied she had been fired and said she gave up the title herself.
"The duties of a world beauty are wonderful. However, my prime goal is my studies and career in Russia," Fedorova told RTR state television. "I know I will remain Miss Universe for Russian citizens and for myself."
She, too, denied she was married or pregnant.
"I want a family, I love family, but it is a dream for me," she said. "I was never married."
Fedorova's victory in May led newscasts across her country. She was pictured firing weapons with perfectly manicured nails and walking police academy halls, dark hair flowing over her drab uniform.
As the winner, she was eligible for prizes worth about $250,000, in addition to promotional contracts, a scholarship and a salary.
The pageant is co-owned by New York real estate mogul Donald Trump.
"It's too bad it didn't work out better with Oxana but our new Miss Universe is equally beautiful and she is a tremendous crowd pleaser," Trump told the New York Post. Trump's spokesman said he would not comment further until after the press conference.
The Post reported that Fedorova was expected to travel extensively and make personal appearances as part of her reign but refused to take part in a number of those assignments, including the 2002 Miss Teen USA Competition.
Fedorova was bestowed with the diamond- and pearl-encrusted crown on May 29 in Puerto Rico.
A show business perennial launched by a swimsuit company 51 years ago, the Miss Universe pageant draws an estimated global television audience of 600 million people in 176 countries.