The headline ISM non-manufacturing index fell to 54.4 in March from 56.0 in February.
Economists expected a smaller drop to 55.5.
Any number above 50 indicates expansion, so this reading indicates that the pace of expansion in the American services sector slowed in March, but remains robust.
The index was led lower by the prices sub-component, which tumbled 5.8 points to 55.9 from 61.7 last month.
The employment sub-component fell 3.9 points to 53.3 from 57.2 last month, and the new orders sub-component decreased 3.6 points to 54.6 from 58.2 last month.
Below is a full breakdown of the sub-indices in the report:
