Activity in the country's services sector last month rose at the softest rate in three months, according to the latest Purchasing Managers' Index from AIB.
The report said the fourth quarter of the year as a whole recorded the strongest growth since the second quarter of 2023.
AIB said there was also a slowdown in business growth in December, which eased to a three-month low, while employment rose only modestly.
The report said inflationary pressures moderated last month but it said charges for services were "still hiked at a relatively elevated pace."
The seasonally adjusted AIB Ireland Services Business Activity Index dipped from November's 42-month high of 58.5 to 54.8 in December.
A reading above 50 indicates an overall increase compared to the previous month and below 50 an overall decrease.
The Services PMI said the latest figure "signalled the softest rate of expansion in output since last September, but one that was still solid and broadly in line with the long-run survey average" since 2000 of 55.
It showed the fourth quarter as a whole "registered the fastest growth since the second quarter of 2023, although on an annual basis growth in 2025 was the slowest since 2020."
Financial Services (63.7) recorded the sharpest increase in activity of the four broad sectors.
The Technology, Media & Telecoms sector slowed notably (54.2), while Business Services (52.2) posted only modest growth and Transport, Tourism & Leisure (47.3) registered "a renewed decline in activity, the ninth in 2025."
AIB said the easing in growth of total activity "reflected a moderation" in the rate of increase in new business at the end of the year.
"The latest expansion was the softest in three months, but still solid overall and among the strongest in 2025," it added.
It said the new business growth remained broad-based by sector, led by Financial Services.
However, new contracts from international clients rose only modestly, with a decline registered in Business Services.
The report said service providers continued to raise their staffing levels in December.
"Employment has risen continuously since March 2021, except for brief dips last January and August. The rate of job creation was only modest in the latest period, however," it added.
It said the Technology, Media & Telecoms sector recorded a sharp reduction in staffing, contrasting with solid gains elsewhere.
AIB Chief Economist, David McNamara, said the Irish Services PMI for December showed "an easing in growth in the sector."
"This still implies robust growth, driven by gains in current activity, new business and employment," he said.
"Overall, the rate of growth in the Irish services sector continues to outperform the Eurozone, UK and US flash PMIs at 52.6, 52.1 and 52.9, respectively," he added.
On the inflation front, Mr McNamara said input price inflation fell to the lowest level since July.
"However, wages, insurance and energy costs, continued to be cited as cost drivers by Irish firms," he added.
The Services PMI found that Irish service providers remained confident regarding the outlook.
"Looking ahead, firms in the Irish services sector were optimistic on the prospects for expansion in activity levels over the coming 12 months, in line with the nine-month high reached in November," Mr McNamara added.
He said companies pointed to investments, new products, recruitment and recovering EU and UK markets "as reasons for optimism."
