Official figures show that the annual rate of inflation fell back to 4% last month from 4.3% in September.
The Central Statistics Office said lower petrol and diesel prices and falls in the prices of clothes and footwear were the main factors in the fall.
The CSO said the October figures did not include rises in excise duties announced in the Budget, as they took effect after the figures were compiled.
Overall, prices fell by 0.2% compared with September.
There was a 2% fall in prices of clothes and footwear, while lower oil prices and air fares led to a 1.8% drop in transport costs.
Prices of furnishings and household equipment were also lower due to sales.
But education costs rose by 3.6% in the month, while there were also higher childcare costs and house insurance premiums.
