Aer Lingus carried a record 1.138 million passengers in August - up 7.3% on the same month last year.
The airline said its transatlantic traffic was up 16.9% to 173,000 passengers.
Its short haul numbers were also nearly 6% higher at 965,000 from 913,000 the same time last year.
Aer Lingus said its overall passenger load factor for August 2015 was up 2.5 percentage points to 90.3%.
Its short haul load factor increased by 4.4 percentage points to 87.9%.
The airline's long haul load factor dipped by 0.7 percentage points in August but remained extremely high at 93.4% for the month.
Aer Lingus said that total passenger numbers for the month, including Aer Lingus Regional flights which are operated by Stobart Air, was up 5.3% to 1.269 million passengers compared to 1.2 million the same time last year.
