Ryanair carryings leapt by almost 50% last month to reach 15.9 million passengers.
Europe’s largest no-frills airline operated more than 88,850 flights in September.
The passenger load factor rose by 13 percentage points year-on-year to 94%.
The September performance saw annual passenger numbers rise from less than 50 million a year ago to 153 million.
Rival budget carrier Wizz Air reported 4.6 million passengers flown in September, up 52% year-on-year.
The load factor was up by 8.4 percentage points to 87.1%.