Four units of Dublin Fire Brigade were on the scene in the early hours of this morning for a fire that broke out on Scoil Naithí, Ballinteer.
It took the squad three hours to extinguish the blaze which has caused major damage to the school.
Parents of the Gaelscoil students were informed this morning by text that the school will be closed today.
The cause of the fire is unknown and the scene is being preserved for Garda technical examinations.
There were no injuries.