The uncertainties of reference values of specimens, which are used for the verification of the secondary standard Charpy impact test machine, are investigated. To evaluate the uncertainty of the reference values of specimens, the results of the direct verification of the machine and the repeatability of measurement are considered. The uncertainty components estimated from the direct verification are calculated multiplying the uncertainty of each item and corresponding sensitivity coefficient. The repeatability of measurement is estimated from the results of the routine check data of the standard machine. By combining these components, the overall uncertainties of reference specimens are presented at 30, 100, and 160 J levels of absorbed energy.