Trump sued author Timothy O'Brien and Time Warner Book Group over the book "TrumpNation: The Art of Being the Donald." It claimed Trump was worth between $150 million and $250 million.
Trump says the book damaged his reputation and argues that his fortune was closer to $2.7 billion.
The judges wrote that details of Trump's life are matters of public interest and therefore are protected.
Numerous publishers of books, magazines and newspapers had joined the appeal, as well as broadcasters and other media organizations, including The Associated Press.