Property prices increased by 2.8% in the year to May.
That compares to an increase of 3% in the 12 months to April.
In Dublin, they rose by 0.6%, while outside the capital they were 5.1% higher in the year to May.
House prices are now rising at the slowest pace in nearly six years, the figures released by the CSO reveal.
However, prices are still lower than before the crash.
Overall, the national index is 18.2% lower than its highest level in 2007. Dublin residential property prices are 21.9% lower than their February 2007 peak, while residential property prices in the rest of Ireland are 21.8% lower than their May 2007 peak.
Since the recovery began, property prices nationally have increased by 82.6% from their trough in early 2013.
Dublin residential property prices have risen 93.4% from their February 2012 low, whilst residential property prices in the Rest of Ireland are 79.9% higher than at the trough, which was in May 2013.