Turner, described in his company biography as a "philanthropist, environmentalist, bison rancher and an avid outdoorsman," will remain on AOL Time Warner's board of directors.
"Over the past five years, it has become even clearer to me how much personal satisfaction I derive from these activities," Turner, 64, said in his resignation letter. "Therefore, I would like to now devote even more time, effort and resources to them."
AOL Time Warner's chief executive officer, Dick Parsons, said in a company statement that he would "continue to rely on Ted's wisdom and advice and know that it will serve our company will in the years to come."
"Ted's leadership role in the formation of global media in general and AOL Time Warner in particular is uniquely significant," Parsons said. "His values of journalistic independence and public service are a permanent part of who we are and what we do."
The company announced Turner's resignation after market close. Shares stood at $13.96, up 30 cents or 2.19 percent, at market close. In 1980, Turner founded CNN, at that time the first around-the-clock, all-news network.
Turner's resignation is the latest move in a series of shakeups at AOL Time Warner, the world's leading media and entertainment company. Earlier this month, Steve Case announced he will step down from his post as company chairman.