Small specimen test techniques (SSTT) for the evaluation of irradiation embrittlement of reactor pressure vessel steel (RPVS) is considered to be essential to operate light water reactors over 40 years old. In this research, specimen size effects were investigated for RPVS to apply small specimen test technique to surveillance test method. Specimens used in this study were machined from a welded A533B steel plate for RPV. Different size of specimens, Standard, CVN-1/2, CVN-1/3, and CVN-1.5 mm were fabricated from the weld bond. It was found that the ductile-to-brittle transition temperature (DBTT) and upper shelf energy (USE) were reduced by decreasing specimen size. The effect of notch position on DBTT was independent of specimen size.