Economists had estimated a reading of 53.4, down from 54.0 in May, according to Bloomberg.
"Purchasing managers are reporting the slowest rate of manufacturing expansion for over a year and a half, suggesting that the economy is slowing again," said Chris Williamson, Markit chief economist, in the release.
"The slowdown is largely linked to a third consecutive monthly fall in exports, in turn attributed by many companies to the strong dollar undermining international competitiveness," Williamson further said.
The report noted that manufacturers reported a slowdown for a third straight month.
However, the pace of growth in payroll numbers was at the highest level since September 2014. "In some instances, survey respondents noted that difficulties in recruiting suitably skilled staff had contributed to rising volumes of work outstanding," the release stated.
The reading is still above the 50 - the mark between expansion and contraction.
Here's the latest chart of the index, showing a slowdown in recent months:
Markit