Winfrey has been hosting the show since 1986.
Although a spokesman for Winfrey''s Harpo production company didn't say why she had made the decision, buzz is that the talk show host plans to launch her own TV channel.
The BBC's Richard Lister in Washington says the show's open atmosphere and frank conversation redefined the talk show genre and made Winfrey the wealthiest black woman in the world, reports BBC News.
OWN, the Oprah Winfrey Network, is scheduled for launch in 2011.
Photograph: Frank Polich/Reuters