Republican presidential nominee Donald Trump declared a US$916 million loss on his income tax returns in 1995, the New York Times reports.
The newspaper said the tax deduction was so major, it could have allowed him to legally avoid paying federal income taxes for up to 18 years.
The New York Times said it had obtained the 1995 records from an anonymous source which had never previously been disclosed.
It says the tax benefits came from the "financial wreckage" of three mismanaged casinos in Atlantic City, Trump's purchase of the Plaza Hotel in New York and his "ill-fated foray into the airline business".
The New York Times wrote: "Although Mr Trump's taxable income in subsequent years is as yet unknown, a US$916 million loss in 1995 would have been large enough to wipe out more than US$50 million a year in taxable income over 18 years."