Markit/ADACI's services purchasing managers' index (PMI) for Italy climbed to 54.6 in August from 52.0 in July. It was the highest level since March 2010.
A reading above 50 indicates expansion in the sector.
The increase was driven by a rise in employment and new business.
"Data showed companies in the service sector creating jobs again after a brief hiatus during July, encouraged by growth in their backlogs of work. A slower increase in new business and a deterioration in companies' future expectations pose some downside risks to the pace of growth in the near-term, however," an economist at Markit Phil Smith said.