Electron tomography has developed into a powerful technique to image the 3D structure of complex materials with nanometer resolution. Both, TEM and HAADF-STEM tomography exhibit tremendous possibilities to visualize nanostructured materials for a wide range of applications. Electron tomography is not only a qualitative tool to visualize nano¬structures, but recently electron tomographic results are also exploited to obtain quantitative measurements in 3D. We evaluated the reconstruction and segmentation process for a heterogeneous catalyst and, in particular, tried to assess the reliability and accuracy of the quantification process. Furthermore, a quantitative analysis of electron tomographic results was compared to macroscopic measurements.