The headline consumer price index (CPI) declined by 3.44% in May from a year earlier, the biggest contraction in nearly 11 years and more than expected, commerce ministry data showed on Thursday.
The reading compared with a forecast decline of 2.95% in a Reuters poll, and with April's 2.99% fall.
The annual core inflation rate was 0.01%, compared with a forecast of 0.35%, and April's 0.41%.