He said he will continue as CEO and be involved in major decisions. However, he appointed Tim Cook to be responsible for all day-to-day operations.
Here is the text of the e-mail that Apple Inc. CEO Steve Jobs sent to employees to announce he was taking a medical leave:
"At my request, the board of directors has granted me a medical leave of absence so I can focus on my health. I will continue as CEO and be involved in major strategic decisions for the company.
"I have asked Tim Cook to be responsible for all of Apple's day to day operations. I have great confidence that Tim and the rest of the executive management team will do a terrific job executing the exciting plans we have in place for 2011.
"I love Apple so much and hope to be back as soon as I can. In the meantime, my family and I would deeply appreciate respect for our privacy."
Cook also served as Apple CEO for several months in 2009 when Jobs, a pancreatic cancer survivor, took a six-month medical leave for a liver transplant.
It was Cook's second stint leading Apple. Cook, who joined Apple in 1998, ran the Cupertino, Calif.-based company for two months in 2004 while Jobs recovered from surgery for pancreatic cancer. His performance then won him the promotion to chief operating officer in 2005.
The Associated Press contributed to this report.