The correlation between subsize and full-size Charpy impact properties of reactor pressure vessel steels have been investigated using 1/3 and 1/4 subsize specimens cut from the broken halves of full-size specimens irradiated to 2.7 × 10²³ n m^-2 (E>lMeV) at 288 °C. We found that ductile-to-brittle transition temperature (DBTT) and upper shelf energy (USE) of subsize specimens have good correlation with those of full- size specimens irrespective of steel types and irradiation conditions, and the shift in the DBTT due to irradiation embrittlement is independent of specimen size. In addition, 1/4 size Charpy data have more scatter than 1/3 size data. Based on the results, we propose a new method to correlate the absorbed energy curve obtained by the subsize test with that by the full-size test. This correlation method is capable to predict adjusted reference temperatures and USEs used in surveillance test programs.