Abstract: Highly accurate mass measurements require correction of mass differences introduced by the difference in center-of-mass height between the measured weight and the reference weight and therefore require measurement of the center-of-mass height of the mass standard. The center-of-mass height can be obtained by placing the mass standard in different positions on the weighing bridge with different orientations and calculating the change in the indicated value of the mass measurement instrument. In this paper, the uncertainty assessment of the 2 center-of-mass height measurement methods is studied, the source of each uncertainty is analyzed, the uncertainty evaluation method is given and discussed in conjunction with examples.