An exit poll projection broadcast by state-financed NOS television said the referendum failed by a vote of 63 percent to 37 percent. The turnout was 62 percent, exceeding all expectations, the broadcaster said.
Although the referendum was consultative, the high turnout and the decisive margin left no room for the Dutch parliament to turn its back on the people's verdict. The parliament meets Thursday to discuss the results.
The constitution was designed to further unify the 25-nation bloc and give it more clout on the world stage. But the draft document needs approval from all the nations to take effect in late 2006, and the "no" vote in both France and the Netherlands founding members of the bloc was a clear message European integration has gone awry.
When voting began, Prime Minister Jan Peter Balkenende said he was optimistic the electorate would defy the pollsters and vote on the merits of the constitution rather than their general feeling of malaise.
"The question is: Do we want to have progress today or do we choose a standstill, and for me the choice is obvious," he said.
But voters marking paper ballots with red pencils or pushing electronic buttons appeared to have a different view.
At an Amsterdam school, where about a dozen people waited to vote, a reporter had difficulty finding anyone in favor of the constitution. One said the charter would bolster Europe: "I think it's a good thing if there's a strong Europe," said Jaena Padberg. "It's good that our rights will be secured."
Some voters said that they were undecided up to the last moment and that it was one of the toughest choices they had faced in a polling booth.
"I can't decide because I don't feel I have enough information," said waitress Flora de Groot, who was determined to vote anyway. "At first I thought, yes, definitely. But now, because what I've heard from other people, I'm leaning toward no."
Opponents said they feared the Netherlands, a nation of 16 million people, would be overwhelmed by a European superstate even though the Dutch pay more per capita than any other country into the collective EU kitty.
Nicolas Ilaria, an immigrant from Suriname, said he was voting no. "In principle, I'm against bureaucracy and I don't believe everything is working well now," he said as he read a newspaper at an Amsterdam cafe.
Like many others, Ilaria voiced an underlying mistrust of Dutch politicians. "The government is not telling the truth about what is in the treaty," he said.
Others were concerned a strengthened Europe could force the liberal Dutch to scrap policies such as tolerating marijuana use, prostitution and euthanasia. Still others said they felt cheated by price increases after they traded in their guilders for the EU's common currency, the euro, in 2002.
"Things are going too fast," said Maarten Pijnenburg, in the "no" camp. "There's not enough control over the power of European politicians" under the new constitution.
The Dutch vote was not expected to have the same dramatic result for domestic politicians as France's referendum Sunday a loss that was a public humiliation for President Jacques Chirac and resulted in Jean-Pierre Raffarin's resignation as prime minister.
Balkenende said before the vote that there would be no political resignations, no matter how the vote went.