The slide into deflation is a sharp reversal from the revised 0.3% increase recorded in January.
It is the first fall in inflation since September when it shrank by 0.1%, according to Eurostat.
Energy drove the decline, with prices down 8% in February compared to a 5.4% slide in January.
The dismal figures have dashed hopes that ECB efforts to boost prices were working. That raises the chance of the bank announcing further stimulus measures next month.
It has already announced a cut to its bank deposit rate, which remains in negative territory.
ECB chief Mario Draghi insisted earlier this month the policies were working.
It's not the first time the eurozone inflation had slid below zero, and once again the price falls are driven by lower energy costs.  But the weakness is widespread.
The breakdown from the EU's statistical agency (not a very detailed one) shows every category having lower inflation than in the previous month. The highest, for services, is just 1%, which is well short of the European Central Bank's target of below but close to 2%.
The ECB has already decided to review its policy next week. The deflation news adds to the chances that the review will lead to more action to get inflation back up (yes, up) towards the target.
That means some combination of more quantitative easing - buying financial assets with newly created money - or taking some of the ECB's interest rates even further below zero.
Nordea economist Holger Sandte said: "Deflation would be a disaster for the euro area as the burden of high debt would increase. Therefore, the ECB will continue easing monetary policy significantly.
"But no matter what the ECB decides to do on 10 March, inflation is likely to hover around zero during the next few months before it picks up - if oil prices behave well."
Economic sentiment across the eurozone deteriorated more than expected in February, according to research by the European Commission.
The Group of 20 (G20) finance ministers and central bankers agreed on Saturday to use "all policy tools, monetary, fiscal and structural - individually and collectively" to renew growth.

Sum: Consumer prices in the eurozone fell sharply in February to minus 0.2%, putting more pressure on the European Central Bank.


Events have moved fast. An afternoon of talks, a new offer, a strike, and a deadline - which passed followed by the dramatic planned imposition of a new contract.
Then came a row over whether there was wider support among NHS leaders over the government's stance.
So where next?
Government negotiators felt they had made a significant move late on Tuesday with a new offer to the British Medical Association.  This would have extended the proposed premium payment for Saturday working from doctors doing one weekend in three to one in four.
But the BMA argued it did not cover the other 50% or so of doctors who did fewer weekends, and so would not qualify for extra payments for working on a Saturday before 17:00.
Wednesday's strike, affecting routine and non-urgent care at English hospitals, continued with no word of the offer or a BMA response.
Late in the evening, details emerged with the important revelation that the government's chief negotiator, Sir David Dalton, had given the BMA a deadline, which had passed.
The union's failure to back the offer, Sir David argued, represented the end of the road for negotiations.
The logical consequence of Sir David's statement was that Health Secretary Jeremy Hunt would feel able to impose a new contract on junior doctors.
There was speculation on whether that might happen within days. In the event it happened with hours of the strike ending at 08:00 on Thursday morning.
Sir David's involvement has been very important for the health secretary.
Mr Hunt has been able to argue that a respected hospital chief executive (Sir David runs Salford Royal Foundation Trust) has done all he possibly could to reach a settlement and that his impartial judgement on ending the talks should be respected.
Sure enough, Mr Hunt could quote Sir David's advice in the House of Commons as he announced his plan to impose the contract from August.
Sir David's letter advised the government to "do whatever it deemed necessary to end uncertainty for the service and to make sure that a new contract is in place".
He said this position was supported by trust chief executives across the country and twenty of their names were added to the letter.
The involvement of a wider group of NHS leaders gave the government further comfort as ministers embarked on their controversial imposition plan.
But late on Thursday, this began to look fragile as the Health Service Journal discovered that some of the 20 named in the letter did not actually support the imposing of the contract.
A bizarre series of exchanges on Twitter flushed out more chief executives distancing themselves from the government's policy - bringing the total to 10 out of 20 according to HSJ.
One of them, Andrew Foster, of Wrightington, Wigan and Leigh NHS Trust, even suggested he had supported a different letter to the one published.
Sir David later told the journal the statement the signatories agreed to was confirming the final position was fair and reasonable, and not signifying support for imposition of the contract.
The Department of Health said this was not a matter for them but for NHS Employers.
It all might prove to be a storm in a teacup with the Dalton letter and its supporters forgotten in a week's time.
But it is an unfortunate development as the government embarks upon what may prove a long-haul in their task of finalising and pushing through the contract.
Ministers certainly will not want to see support at senior levels in NHS management melt away as they move into uncharted waters with contract imposition.
A noisy gathering of junior doctors at Westminster on Thursday night showed that they were not winding down their campaign against the contract.
The BMA is planning its next move, which might involve further industrial action.
It may be a long, hot summer for the government as it tries to win public support for a move that has angered an important constituency in the medical profession.

Sum: After weeks of uncertainty - and both sides eyeing each other suspiciously from a distance - the junior doctors' row has moved to a new level this week.


Fuel duty has been held at 57.95p per litre since the March 2011 Budget.
In his Autumn Statement, Mr Hammond also revealed plans for investment in transport, including £1.1bn for English local networks.
And he pledged £390m for work on low emission vehicles and the development of connected autonomous vehicles.
Fuel duty remains the biggest component of the price of diesel and petrol. Motorists also pay 20% value added tax on those fuels.
It was last increased in January 2011 from 58.19p to 58.95p a litre and cut by a penny in the Budget two months later.
Mr Hammond said: "This will save the average car driver £130 a year and the average van driver £350 a year.
"It is a tax cut worth £850m next year and means the current freeze is the longest for 40 years."
What the Autumn Statement means for you
UK economy 'resilient' despite £122bn hit
Autumn Statement latest updates
Key points at-a-glance
Your questions answered
Drivers could also find their journey times cut after the chancellor announced investment of £220m to "address traffic pinch points on strategic roads".
He also promised £110m for an Oxford to Cambridge Expressway as well as East West Rail to create "a transformational tech-corridor" to link "the world-class research strengths of our two best-known universities".
In addition, the government will invest £450m to trial digital signalling on the railways to "achieve a step change in reliability and to squeeze more capacity out of our existing rail infrastructure".
Mr Hammond added: "Reliable transport networks are essential to growth and productivity so this Autumn Statement commits significant additional funding to keep Britain moving now and to invest in the transport networks and vehicles of the future."
He said the money for low emission vehicles would "build on our competitive advantage" in the field.
The chancellor added that the Department for Transport would continue to work with Transport for the North to develop detailed options for the Northern Powerhouse rail system.

Sum:
Next year's planned rise in fuel duty has been cancelled by Chancellor Philip Hammond - the seventh successive year that the tax has been frozen.