It is empirically known that the flowability of ground powders varies with the types of mill. In this study, five kinds of test powders of the same size made from the raw material were prepared by five different types of mills and classifiers. The flowability of these powders was measured and the difference between each result identified. Then, the relationship between the flowability of the powder and particle shape was investigated. The circularity, Wadell＇s working sphericity, the fractal dimension of particle perimeters and the specific surface area ratio of the test powders were measured, and the effect of the particle shape on the flowability index was studied. The result was that the particle shape, especially the surface roughness of particles, had a very great effect on the flowability of the powders produced in different types of mill.