Obama's success is surprising in that he has rivalled Clinton despite the huge fund-raising network she developed through her senate campaigns and the contacts of her husband, Bill Clinton, the former president.
Obama said: "It means we've got broad-based support, and I'm very proud of that."
The Illinois senator said he was proud of the amount considering it was raised without the aid of lobbyists.
In an email message to supporters, Obama said his fundraising success represented "an unmistakable message to the political establishment in Washington about the power and seriousness of our challenge".
Former senator John Edwards of North Carolina said he had raised more than $14 million during the first three months of the year, nearly twice that of the first quarter of his failed 2004 Democratic presidential bid.
The Clinton campaign congratulated Obama and all Democrats seeking to succeed George Bush, the current US president.
Patti Solis Doyle, Clinton's campaign manager, said: "We are thrilled with our historic fund-raising success and congratulate senator Obama and the entire Democratic field on their fund raising."
But the surprisingly strong haul for Obama was a huge boost for the relative newcomer and only black US senator.
Stephen Hess, a George Washington University professor, said: "They will have to look for ways to distinguish themselves from each other."
"No one is locking it up now."
While Republicans have usually raised more than Democrats, in the 2006 mid-term elections they were relatively evenly matched and Democrats won control of the congress.
On the Republican side, Mitt Romney, the former governor of Massachusetts, raised $20.6 million in 2007 while the man leading in most national polls, Rudolph Giuliani, the former mayor of New York, raised $15 million.
Costas Panagopoulos, a political science professor at Fordham University, said: "In an era with an unpopular Republican president, an unpopular war, it's going to be tough for the Republicans to raise money."
Senator John McCain of Arizona, who ran in 2000, raised $12.5 million for his campaign.