The published measurement data of atomic weight of uranium are shown in table 4^[9]. The best results are those measured by Smith and Cowanet al. A _r (U) = 238.028 79–238.028 90(3), their result error being ISD. The evaluated value of IUPAC-CAWIA is A_r(U)=238.028 9(1). In this work, the result is A_r(U) = 238.028 91(4). The combined uncertainty has been given according to 2SD of the measurement data through the calibration of a series of standard materials of uranium isotopes. It is reasonable to conclude that in this work the uncertainty which characterizes the measurement quality is better than other published data.