Winfrey introduced the Precious star at this week's Oscars and predicted a bright future for the actress.
During her tribute, Winfrey described Sidibe as "a true American Cinderella on the threshold of a brilliant new career".
She added: "And 'precious' is but the first of many adjectives coming your way - and they are all great."
"I saw myself in her," Winfrey told People. "This whole rollercoaster that happens to you when you're passionate about something - she wasn't even thinking about being an actress, she just auditioned.
"And now here she is, being nominated alongside Meryl Streep, who is the greatest actress in the world, with Sean Penn reading her name. Only in America."