A retainer for a gas turbine blade that inhibits deviation of a rotating blade mounted on a rotor of a gas turbine, can include: a retainer frame disposed at one side of the rotating blade and configured to form an inside chamber through which cooled air is introduced, between the retainer frame and the rotating blade; a barrier wall formed between the retainer frame and the rotating blade and configured to divide the inside chamber into a plurality of cooling chambers; and a fixing unit disposed at one side of the retainer frame and configured to fix the retainer frame to the rotor.