The multimillionaire Romney has been under pressure from his rivals for the Republican presidential nomination and others to release the information.
Speaking to reporters Tuesday in South Carolina, Romney said most of his income comes from investments, not regular wages and salary. The tax rate on investment income is 15 percent, much lower than the 35 percent rate applied to wages for those in the highest tax bracket.
He suggested he would release only one year of tax information, for 2011.
Romney had initially said he would not release the tax returns.
The White House is suggesting Romney should release his tax returns, saying it's "established tradition" for presidential candidates to do so.
Responding to a question about Romney's failure so far to release his returns, White House press secretary Jay Carney stopped short of directly calling on the former Massachusetts governor to make them public. But he noted that when Barack Obama was a presidential candidate he released multiple years of his returns.