Aer Lingus said it carried a record 1.13 million passengers last month, up 7.3 per cent on the 1.06 million carried in August 2014.
Total passenger numbers - including Aer Lingus regional flights - was up 5.3 per cent to 1.26 million as against 1.20 million a year earlier.
Aer Lingus said transatlantic traffic continued to grow strongly with passenger numbers up 16.9 per cent year-on-year to 173,000 versus 106,000 for August 2014.
Short-haul passenger numbers were up 5.7 per cent over the same period from 913,000 to 965,000.
Load factor - a measure of how full flights are - was up 2.5 percentage points to 90.3 in August as against 87.8 a year earlier.
Short haul load factor was up 4.4 percentage points to 87.9 per cent while long-haul load factor, while marginally down 0.7 percentage points last month, was still high at 93.4 per cent for the month.