This paper investigated uncertainty model of random-incidence scattering coefficient measurements for understanding reproducibility and repeatability. Uncertainty model was derived based on measurement procedure specified in ISO 17497-1. Uncertainty components were categorized as Type A and Type B. As results, standard uncertainty and sensitivity coefficients of the proposed model were suggested with an example of scattering coefficient measurements. In addition, some methods for improving reproducibility and repeatability of scattering coefficient measurements were discussed.