We examined the mixing process of oral solid medicines and considered the method of validation for content uniformity: 1) the suitability of mixing time, 2) the mixing degree in the multi-step mixing processes and 3) the differences in sampling methods. The data were obtained from two manufacturing factories (Model I and Model II). Model I utilizes about one-step mixing operation for powder preparation, while Model II utilizes multi-step mixing processes required prior to tablet preparation. While the validation of manufacturing pharmaceutical preparations is generally invested in each manufacturer, the results of this study may offer useful information of the mixing operation of medicinal powders in terms of the mixing time, selection of container, and sampling tools.