A structure for assembling turbine blade seals, a gas turbine including the same, and a method of assembling turbine blade seals are provided. The structure for assembling turbine blade seals includes a turbine blade including an airfoil, a platform, and a root, a turbine rotor disk to which the root of the turbine blade is mounted, a seal plate mounted between the platform and one side of the turbine rotor disk to seal a cooling channel defined within the root and the platform, an insertion pin inserted through the turbine rotor disk and the seal plate to fix the seal plate to the turbine rotor disk, and a retainer configured to fix the insertion pin and to prevent the insertion pin from falling out.