The latest traffic statistics for Aer Lingus show that the airline flew 734,000 passengers last month, an increase of 7.2% on December 2011.
The figures include the airline's regional operations.
Aer Lingus' short haul passengers figure came to 658,000, an increase of 6.5% on December the previous year; while long haul passengers last month were 76,000, an increase of 13.4% on December 2011.
The airline's load factor - or how many seats it filled on each flight - increased as capacity fell. December's overall load factor increased by 2.9 points to 70.9%.
Its short haul load factor inched 0.7 points higher to 66.6%, while its long haul load factor rose by 6.1 points to 77.7%
Ryanair passengers stats up 2%
Ryanair carried 4.84 million passengers in December, a 2% increase on the same month in 2011.
For the year to the end of December the airline flew 79.6 million passengers, up 4% on the previous year.
Ryanair's load factor, the percentage of seats filled, was 81% in December compared to 79% in the same month a year earlier.