The so-called biblical Rapture was interpreted as the end of the world.
Harold Camping, 89, was hospitalized in Alameda Thursday.
A radio station spokesman says Camping suffered the stroke at his home last Thursday. Doctors say Camping is making progress. No details about his condition were made available.
Camping's media empire spent millions of dollars, some of it from donations made by followers, publicizing the evangelist's Rapture prediction over the past seven years.
When the apocalypse failed to occur on May 21, Camping was widely mocked and he called it "a very difficult time."
He has since insisted that his prediction was overall correct. On May 24 he clarified that a "spiritual" Judgment Day had begun three days earlier, placing the entire world under Christ's judgment, and said the Earth actually would be obliterated on Oct. 21.
The Associated Press contributed to this report.