Bulgaria's EU-harmonised consumer prices rose by 1.8% on the year but were 0.1% lower month-on-month in May, the National Statistics Institute (NSI) said.
In April the consumer price index (CPI) increased by a monthly 0.2% and by an annual 2.0%.
The inflation rate since the beginning of the year stood at 1.2% in May, NSI said in a statement on Tuesday.
The price index of the small basket in May fell 0.2% on the month while the overall increase since the beginning of the year stood at 1.5%.
Bulgaria's non-EU harmonised monthly CPI also fell by 0.1% on the month and was 1.7% higher on the year in May. In April it was 0.2% higher than a month earlier and 1.7% up on an annual basis.