The multi-billionaire made the announcement on his Facebook page Tuesday afternoon, saying that he and his wife Priscilla have "made a contribution of 18 million Facebook shares to the Silicon Valley Community Foundation" as part of a pledge to donate most of their wealth to charity.
The Mountain View-based foundation funds a wide range of nonprofits and charities and declined to say how the money might be spent.
With Facebook's stock price at $27.71 today, the contribution is valued at $499 million. That is slightly more than the $470 million in total donations the SCVF received in all of 2011.
"This is the Silicon Valley Community Foundation's largest single gift," said Rebecca Salner, vice president of marketing and communications for the SVCF.
It is reportedly also Zuckerberg's largest donation yet.
In his announcement on Facebook, Zuckerberg says that he and his wife signed "the Giving Pledge" two years ago, an effort started by Bill Gates and Warren Buffett which now has 81 billionaires pledging to donate most of their wealth to charities.
"Our first major project has been around education reform with Startup: Education in Newark, NJ," Zuckerberg writes in his announcement. "I'm really proud of the work we've done there, helping leaders like Governor Chris Christie and Mayor Cory Booker sign the most progressive teachers contract in our country, opening four new district high schools, 11 new charter schools and more."
"Today, in order to lay the foundation for new projects, we've made a contribution of 18 million Facebook shares to the Silicon Valley Community Foundation," Zuckerberg wrote. "Together, we will look for areas in education and health to focus on next. I'm hopeful we'll be able to have as positive an impact in our next set of projects."
Foundation officials were tight-lipped about the donation, other than issuing a brief statement.
"Mark's generous gift will change lives and inspire others in Silicon Valley and around the globe to give back and make the world a better place," said Emmett D. Carson, CEO of Silicon Valley Community Foundation. "We are pleased and honored that he has chosen to continue to partner with us to help him achieve his philanthropic goals."
Zuckerbeg, who draws a $1 a year salary from Menlo Park-based Facebook, had an estimated net worth of $9.5 billion earlier this year, according to Forbes magazine.