Inflation in the 12 countries using the euro rose to 2.5 per cent year-on-year, the European Union's statistics office estimated, up from 2.4 per cent in April.
The Eurostat estimate does not include any details or monthly figures.
Meanwhile, economic sentiment in the euro zone rose to 106.7 points in May from an upwardly revised 105.7 in April, the European Commission said. It was the highest reading since April 2001, and economists had expected an easing to 105 points.
The upbeat sentiment data and rising inflation are likely to reinforce the case for an ECB rate rise. Economists expect the cost of credit to increase by 25 basis points to 2.75 percent, but some do not exclude the possibility of a 50 bps rise.
The ECB has said it would raise rates to stem inflationary pressures from high oil prices and fast credit growth as the euro zone economy accelerates.
The bank wants to keep inflation below but close to 2 per cent, but the Commission survey showed a strong rise in inflation expectations among consumers in May.
The improvement in overall economic sentiment was thanks to 1-point rises in confidence in the industry and services sectors and among consumers, who have become more optimistic about their job prospects.
The biggest rises in consumer confidence were in Germany and Italy, two of the euro zone's three biggest economies.
In industry, the confidence indicator rose to 2 points in May, just 4 points short of a historic high recorded at the peak of the dot-com bubble in May 2000.
The Commission's business climate index, which points to the phase of the business cycle, eased slightly from April but remained at January 2001 levels, "suggesting that the pick-up in industrial production growth should continue in the second quarter of 2006".