Ryanair said it carried a total of 9.5 million passengers in December, up from 1.9 million the same month last year and in line with its forecasts.
The airline said it operated over 62,200 flights in December.
It also reported an 81% load factor - how many seats it fills on each flight - for December.
Last month Ryanair more than doubled its annual loss forecast and cut its January traffic forecast by 33% due to the impact of the Omicron variant of Covid-19.
The airline, which is Europe's largest by passenger numbers, said in a statement that it expects a net loss of between €250m and €450m in the 12 months to the end of March.
That compares to a previous forecast of a loss of between €100m and €200m.
The airline also cut its January traffic forecast to between 6 and 7 million, from 10 million.
