Micro computed tomography (mu CT) is proposed as a tool for the characterization of powders. Using this technique three dimensional images carrying the whole spatial information on a particular powder can be obtained. After an image analytic separation of the single particles, distributions of geometric characteristics describing size, shape, and spatial arrangement of the particles can be estimated. The method is applied to four samples of powders with different particle structure. The results are compared with particle size characteristics measured by laser diffraction, sieve analysis, and the analysis of microscopic 2D images.