More than two-thirds of eurozone citizens expect to be cheated on prices, according to the new survey.
The EU poll of more than 6,500 people shows that 70% are concerned about prices being jacked up in the early days of the single currency launch.
And nearly 50% are worried that they will face difficulties in dealing with the currency in their daily lives.
The poll, conducted at the end of November, showed that 85% understand that the euro will be immediately accepted and can be used in other euro zone countries.
But as a Commission spokesman pointed out: "This means that there are still 15% who have not grasped the very meaning of the single currency".
About 40% said they can already remember prices in euro and 67% know its exact value in their national currency.
Four practical advantages of a single currency were highlighted by the vast majority: it should make travelling easier (90%); it will make purchases easier in the 12 countries (87%); it will make comparing prices between countries easier (78%); and it will eliminate exchange costs (66%).
The suggestion that the euro will acquire the status of an international currency alongside the dollar was accepted by 61%, while 59% think it will help keep prices stable and 58% said it will promote economic growth in the eurozone.
Nevertheless only 48% believe that the euro has more advantages than disadvantages, while 40% think the opposite. The rest don't know.
In the three EU countries not in the eurozone - Britain, Denmark and Sweden - a survey of 1,500 people showed that 79% are convinced that their national currencies will eventually be replaced by the euro.