The shape of inorganic powder particles, prepared by spray-drying process, is close to sphere, and the dry conditions have greater effect on the sphericity. The particle shape is normally described by words or shown by micrographs — these are qualitative and imprecise. In order to characterize the particle shape quantitatively, three shape factors, i.e. aspect ratio (M), roundness (R) and concavity (C), are proposed to describe the particle shape of the inorganic powders in different aspects. An image process method, that “holes” were filled and then particle clusters were separated, was developed and applied in scanning electron microscope (SEM) image in which some particles with “shadow” contact with each other. Mean shape factors, based on about 500 particles in 10 micrographs, are proposed to characterize the particle shape of the inorganic powders. The determination results of four inorganic powders show that cracking catalyst powders without silicon additive and produced after rebuilding of the spray-drying device are closer to spheres.