The headline Purchasing Managers' Index for manufacturing -- with figures above 50 indicating growth -- slipped from a 33-month high in November at 58.1 to 57.3 in December, Markit said.
The new reading is "still a level indicative of a robust improvement in overall operating conditions," Markit said.
For the final quarter of 2013, the average monthly PMI level was 57.2, the highest level for a quarter since January through March of 2011.
Output and new order growth "remains robust," Markit said.
Prices producers paid for materials and received for their goods both rose at a faster pace in December compared to the pace in the previous month.
"On its current track, the sector should achieve output growth of over 1 percent in the final quarter while filling around 10-15 thousand jobs, continuing its positive contributions to both the broader economic and labor market recoveries," said Rob Dobson, senior economist at Markit.