Winfrey originally planned to retire from the show in 2006

The series began in 1986 and has made Winfrey one of the highest-paid women in US television.

"The thought of taking the show to its 25th anniversary is both exhilarating and challenging," Winfrey, 50, said.

The show has won 38 Emmy awards, been distributed to 107 countries and has been a top-rated talk show in the US for the past 18 years.

Book endorsement

The 50-year-old host originally planned to retire from the show in 2006, but decided to stay after a boost in the show's ratings.

Winfrey's onscreen Book Club also proved a huge success, with her endorsement of a novel ensuring it made the best-seller lists.

Stars celebrated Winfrey's 50th birthday on her show in January

In June, she renewed interest in Leo Tolstoy's Anna Karenina, telling readers not to "be scared" by the book's 837-page length.

Following the chat show's success, Winfrey has earned a personal fortune estimated in excess of �1bn (�548m).

The Oprah Winfrey Show has spawned countless imitations around the globe, with US presenters Maury Povich, Ellen DeGeneres and Wayne Brady tipped as possible future successors to her position.