The Purchasing Managers' Index for the factory sector climbed to 52.4 from 50.8 in April. Economists had expected the reading to remain unchanged.
A PMI score above 50 suggests growth in the sector. The manufacturing sector grew for a tenth month running.
Overall new orders grew for a tenth straight month though export demand declined.
Input prices rose at a historically modest pace and output prices climbed for a second month in a row. Employment declined for a third consecutive month.
"The manufacturing sector continues to make a positive contribution to overall economic expansion, with IHS Markit forecasting GDP growth of 1.1% in 2017, below the official prediction of 1.5-2%," Sian Jones, an economist at IHS Markit, said.
"This follows subdued growth at the start of 2017."
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