IAG, the company which owns Aer Lingus and British Airways, saw a 9.3% increase in the number of passengers carried in December when compared with 2014.
This includes a 6.5% increase in revenue for the group.
IAG airlines carried almost 95 million passengers in 2015.
Aer Lingus joined the IAG stable in August after shareholders voted to accept a takeover following a statement from IAG that Aer Lingus would remain an "iconic Irish brand" with its base and management team in Ireland.
The Government gave the green light to the €1.4bn bid in May last year.
Under the deal, IAG said it has agreed to a number of “legally binding” promises on the future of Aer Lingus, including the development of Dublin as a hub for transatlantic routes.