The daily rankings of the world's 500 richest people listed in the Bloomberg Billionaires Index showed the top 3 remained the same Saturday.
Zuckerberg is now worth $81.6 billion, nearly $400 million more than Buffett, chairman of the Berkshire Hathaway investment group, rankings show.
Zuckerberg's California-based social network business has more than 2 billion active monthly users.
Zuckerberg has pledged to give away 99 percent of his Facebook stock away in his lifetime, his Bloomberg profile shows. Further, Zuckerberg has given $3.58 billion in stock sales away this year alone to a charity initiative he set up with his wife, Priscilla Chan, in 2015.
Buffett has donated about 290 million of his shares in Berkshire Hathaway to charities -- an equivalent of about $50 billion.