The Consumer Prices Index (CPI) grew by 1.5% in the year to May 2014, down from 1.8% in April.
The last time CPI stood at 1.5% was October 2009.
The Office for National Statistics (ONS) said falls in transport services costs, notably air fares, provided the largest contribution to the decrease in the rate.
Other large downward effects came from the food & non-alcoholic drinks and clothing sectors. The largest offsetting upward effects came from motor fuels and recreation & culture.
It also added that the timing of Easter in April is likely to have had an impact on movements in the index, most notably for air and sea fares.
