More than 56% of voters went against adopting the currency, while only 41.8% were in favour.
The government expressed its disappointment at the result, and blamed a bad EU economy for the result.
Deputy Finance Minister Gunnar Lund said calling a referendum at a time of such unattractive eurozone growth rates may have been his government's "biggest mistake".
"Our greatest difficulty was the unfortunate timing of the
campaign," he said. "The entire European Union was going through a very difficult phase, a recession," he said.
Results are likely to disappoint Swedish Prime Minister Goeran Persson, a fierce advocate of the single European currency.
The European Commission insisted it was confident the Swedish government would "keep the euro project alive" but found it hard to disguise its disappointment.
The decisive Swedish "no" vote does not augur well for hopes of convincing other European Union members still outside the euro zone, Denmark and Britain.
Britain's eurosceptics were among the first to hail the Swedish "no" vote, which was more conclusive than expected.
"(The result) highlights the huge difficulty that the government would have winning a vote in Britain, where opposition is even higher," said George Eustice, director of the "no" campaign against British membership of the euro.
Killer at large
Swedish Foreign Minister Anna
Lindh's murder muted debate
Sweden had always looked likely to return a resounding "no" even before Anna Lindh, the popular 46-year-old foreign minister and mother of two, was knifed to death while shopping at a Stockholm department store.
Police hunting her killer circulated security video pictures of a dark-haired man in a baseball cap and grey college sweater.
The man remained at large on Sunday, evoking painful memories of the 1986 assassination of Prime Minister Olof Palme, a few blocks away by gunshot. Palme's killer has never been found.
Politicians suspended all campaigning after Lindh died early on Thursday, and a wave of emotion swept the nation.
Flowers, notes and children's drawings piled up outside the store in central Stockholm, and teary-eyed Swedes paid their respects to the woman who had been tipped as the next prime minister.
Until Lindh's murder, debate had focused on whether the euro would help or hinder Sweden's relative economic advantages over the euro zone - which has higher unemployment and lower growth - and what it would mean for Sweden's cherished cradle-to-grave welfare state, funded by some of the world's highest taxes.
Eurosceptics say handing over monetary tools to the European Central Bank would leave them unshielded from economic shocks, while pro-euro Swedes think joining the final phase of Economic and Monetary Union would boost trade and ensure future growth.
About seven million people were eligible to vote. Turnout in Swedish referendums is traditionally around 80%.