New figures from the Central Statistics Office show that the decline in consumer prices accelerated last month, with a 3.5% annual drop.
This compares with a negative inflation rate of 2.6% in March.
Prices fell by 0.8% in April compared with March, with lower mortgage repayments and falling clothing prices the main factors.
Clothing and footwear prices dropped 3.6% in the month, while mortgage interest costs plunged 13% after lenders passed on the March interest rate cut from the European Central Bank.
Mortgage interest has now fallen by almost 40% over 12 months.
Furnishings and household equipment prices also fell 1.3% in the month due to sales, but Budget increases in cigarette duties pushed up prices in the alcohol and tobacco category.
Transport costs rose 1.1% as higher oil prices fed through to petrol and diesel costs. Petrol prices rose 3.6% in April, while diesel was up 6.5%.
