Irradiation-induced hardening was investigated in reactor pressure vessel steels, A533B, irradiated with 2.8MeV Fe2+ ion dose up to 1dpa with dose rate ranging from 10-5 to 10-3dpa/s at 563K. Alteration of local hardness was intensively measured as a function of dose and dose rate. To evaluate the local hardness, nano-indentation technique was employed to clarify the effect of microstructure, which is ferrite matrix and embedded colonial carbides. Hardening in the regions was observed with increasing dose, φt. Irradiation hardening of carbide colony regions is greater than ferrite regions higher dose than O. 1dpa. Hardening in the both regions is proportional to φt1/2 up to 1dpa. In the carbide colony region, irradiation hardening at the dose lower than 0. 1dpa was greater than that in ferrite region. Effect of dose rate was observed to be more significant at the lower dose in the carbide colony regions.