Oprah Winfrey will host her final talk show in 2011, her production company said, announcing the end of a 25-year run that has made her one of the most influential stars in America.

"The sun will set on the 'Oprah' show as its 25th season draws to a close on September 9, 2011," Tim Bennett, president of Winfrey's Harpo production company, wrote in a letter to affiliates on Thursday.

"The Oprah Winfrey Show", which is currently syndicated in 145 countries, has transformed Winfrey into a cultural phenomenon.

She has been credited with changing the way people talk to each other through her confessional interview style and is regularly ranked among the most powerful women, celebrities and media personalities in the world.

Don Halcombe, a spokesman for Harpo Productions, declined to comment on why Winfrey decided to end the program.

"She's going to talk about it on the show tomorrow," he told AFP.

The New York Times reported that Winfrey is not renewing the talk show so she can concentrate on launching her own television channel.

OWN: The Oprah Winfrey Network is a joint venture between Winfrey and Discovery Communications and is set to replace the Discovery Health Channel in about 70 million US homes.

While originally scheduled to air in 2010, getting the cable channel launched has proved "challenging" due to "management turnover and an uncertain advertising climate," the Times reported.

It is now scheduled to air in January 2011, but Winfrey, who will produce some shows and also make appearances, does not plan to bring her talk show, the Times reported.

Winfrey has transformed her talk show into an empire that spans books, radio, magazines and the Internet.

Her endorsement of fellow Chicagoan Barack Obama was estimated by University of Maryland researchers to have brought in a million additional votes and helped Obama win both the Democratic nomination and the presidency.

She has also pushed scores of books to the top of the best seller's list through her now-defunct televised book club and can spark runs on products with her recommendations.

Born into poverty in Mississippi, Forbes magazine recently estimated Winfrey's net worth at 2.7 billion dollars.