Many ceramic materials are composed of various phases, which can differ in their individual thermal, elastic or electrical properties by orders of magnitude. The microstructural arrangement of the phases controls important material properties of the composite. To simulate these macroscopic material properties from the material properties of the constituting phases, a 3-D FEM model is used. The key for an adequate description of real materials is the accurate threedimensional modeling of their microstructure. Basic morphological parameters of many ceramics are reflected by a modified Voronoi model, e.g.: the volume fractions, grain size ratios and contiguity of the phases. By automatically generating thousands of test structures and comparing them to quantitative data derived from image analysis of scanning electron micrographs, structures are selected which closely fit to the microstructure of experimental samples. The model considerations are illustrated on two types of bi-continuous ceramic materials, a porous alumina (Al2O3) and a dense zirconia toughened alumina (ZTA) ceramic. Using different volume fractions of the phases, Voronoi type microstructures and truncated sphere models are exemplified. For these two ceramic systems, elastic moduli and thermal conductivity are calculated and compared to experimental data of samples of the respective microstructure.