Romney's campaign and the party said they entered this month with $107 million to spend.
The Obama campaign said on its website today that it had raised more than $60 million last month. It didn't offer a cash-on-hand figure.
The figures include money for the presidential campaigns as well as national and state party committees, which can accept much larger donations than candidates. Both Mr. Obama and Mr. Romney have set up joint fundraising committees with the parties.
Mr. Romney is raising money for the general election for the first time, allowing him to go back to the same donors who funded his successful primary campaign.
The 2012 election will be the first since the Watergate scandal-plagued 1972 race in which both major party presidential nominees fund their campaigns entirely with private contributions. Until now, at least one major-party nominee had taken federal funds and agreed to spending limits in every election since 1976, the first under campaign-finance laws enacted in response to Watergate.
"Our strong fundraising is a sign that Americans are tired of President Obama's broken promises and want a change of direction in the White House," Republican National Committee Chairman Reince Priebus said in a statement. "We will continue the hard work of raising the resources to defeat President Obama so that we can elect Mitt Romney and Republicans up and down the ballot to get our country on the right track again."
The Obama campaign touted its 572,000 donors last month as "the grassroots strength of this organization, and a contrast to the special-interest money the Romney campaign is relying on for support."
Details on fundraising by campaign and party committees are due at the Federal Election Commission June 20.
Obama's re-election committee more than doubled the amount raised by Romney's presidential campaign through April, taking in $222.3 million to $100.4 million, and had $115.2 million in the bank entering May, compared with $9.2 million for the challenger.