Aer Rianta has secured the A+ credit rating from Standard & Poors it had been seeking.
The is the State airports company's first such rating because it has loans worth £200 million and has recently secured Government approval to extend its borrowing limit to £350 million from £250 million.
The development means it may be able to secure credit on more favourable terms as its capital investment programme expands.
Aer Rianta also plans to launch a £100 million bond programme before the end of the year.