Markit/ADACI's services purchasing managers' index (PMI) for Italy rose to 53.4 in October from 53.3 in September.
A reading above 50 indicates expansion in the sector.
The increase was driven by a stronger rise in new business.
"Italy's service sector continues to expand at a steady pace, with the headline PMI in October broadly in line with that seen in September and for the third quarter as a whole. Growth in new business strengthened to a six-month high, showing that demand continues to build," an economist at Markit Phil Smith said.