Mrs. McCain, who files her taxes separately from her husband, paid $1.1 million in taxes, a tax rate of about 26 percent. She reported nearly $530,000 in itemized deductions.
The McCain campaign said her losses were in investment income directly related to her family business, Hensley & Co., an Arizona beer distributorship of which she is chairwoman.
"The reduction is a combination of capital investments in the business and, like many companies, Hensley has felt the impact of a weakened economy," McCain spokesman Brian Jones said.
The Arizona senator's campaign had released her 2006 return in May but said Mrs. McCain had requested an extension on her 2007 return.
McCain himself released his own tax return last April, reporting a total income of $405,409 in 2007 and $84,460 in federal income taxes.
Democratic rival and his wife, Michelle, made their returns public earlier this year, reporting $4.2 million in 2007 income, most of it profits from his books, "Dreams From My Father" and "The Audacity of Hope."
The McCain campaign only released the summary pages of Mrs. McCain's returns, thus offering limited information on her finances. She listed nearly $2.9 million in income from rental real estate, royalties, partnerships and trusts - a category that would include her investment income from Hensley & Co. She had reported $4.5 million in that category in 2006.
She also reported $297,000 in salary income, more than $118,000 in dividends and more than $746,000 in capital gains. Her dividend income dropped by about $165,000 from 2006.
Perhaps anticipating higher income, she overpaid her taxes over the year by more than $950,000. She applied that amount to her 2008 estimated tax.
As an heiress to the Hensley fortune, Cindy McCain's worth has been estimated at more than $100 million.