Buffett, who is chairman and chief executive of Berkshire Hathaway, said in a statement he had donated $4.1 billion of his Class A shares to five foundations. He has now given away a total of $41 billion to the five groups.
Buffett, 90 years old, now owns 238,624 Class A shares, valued at about $100 billion.
Berkshire Hathaway Class A shares closed Tuesday at $418,875.
In 2006, Buffett pledged that he would give away much of his fortune over time. In June of that year he owned nearly 475,000 Class A shares of Berkshire Hathaway.
One of the five foundations is the Bill and Melinda Gates Foundation, founded by the former Microsoft (MSFT) - Get Report executive and his wife. In early May, Bill and Melinda Gates said they would divorce after 27 years of marriage.
Buffett also resigned as a trustee of the Gates Foundation. He is not involved in the endowment's investment decisions, Bloomberg reported. He and Bill and Melinda Gates are the only trustees of the foundation.
He said in his statement that the chief executive of the Gates Foundation, Mark Suzman, "has my full support."
His statement on Wednesday is "no swan song. I continue at my enjoyable job, doing what I like, aided by associates I like, and working to deploy the savings of people who have long trusted me."
Among a number of topics the executive raised in his remarks was:
"A much more admirable form of philanthropy than mine involves the giving of personal time and effort. I’ve done little of that.
"Those who give their love and time in order to directly help others – perhaps adding a monetary gift that requires them to give up the purchase of something meaningful for their own use - are the heroes of philanthropy. America has millions of such givers.
"These people receive no recognition whether they mentor the young, assist the elderly or devote precious hours to community betterment. They do not have buildings named after them, but they silently make those establishments – schools, hospitals, churches, libraries, whatever – work smoothly to benefit those who have received the short straws in life."