The 16-nation bloc and its common currency have been hit by waves of investor insecurity churned up by the region's debt crisis and fears that troubles in Greece may be spreading to other peripheral eurozone economies.
“There has been a slowdown in growth globally and in the eurozone there is subdued domestic demand due to the austerity measure implemented in some countries,” said Luigi Speranza at BNP Paribas.
The Markit Eurozone Manufacturing Purchasing Managers' Index for May sank to 55.8 from 57.6 in April, nudged down from an earlier flash estimate of 55.9.
This is its eighth month above the 50.0 mark that divides growth from contraction, but markets were unmoved by the data.
Cost pressures were on the rise, with the price of factories' raw materials forced up by the weaker euro.
The output index recorded its second fastest slide in the survey's history – only surpassed in the aftermath of Lehman Brothers' collapse – to stand well shy of April's near 10-year high of 61.2 at 56.8. It inched up from a flash reading of 56.7.
“Importantly, however, the pace of growth remained robust, and the slowdown in May no doubt reflects a payback from April's ultra-strong growth to some extent,” said Chris Williamson at data provider Markit.
In Germany, the bloc's biggest economy, manufacturing activity slowed from the previous month's survey's record high. Neighbouring France, the second biggest, saw growth in its sector slow from April's near four year high.
Spain and Italy also saw a dip in their main indexes. A separate survey on the UK showed manufacturing activity holding on to its strongest pace in 15 years.
Eurozone manufacturers were hit by rising input prices, with that index reaching its highest level since July 2008 at 73.7 in May, compared to 73.4 in April.
The euro has been battered in recent weeks, driving up costs of materials from outside the bloc, on fears that Greece's debt problems will spread and in spite of a $1trn safety net set up by European policymakers earlier in May.
However, the output price index fell, suggesting producers had more trouble passing on price rises to customers.