Catalytic active coatings for microchannels have been developed for metallic microstructure reactors in heterogeneous catalyzed gas phase reactions. To enhance the inner surface of microchannel reactors, porous metal oxide coatings have been made by various deposition techniques such as sol–gel processes, anodic oxidation, and deposition of nanoparticles. The ceramic thin films have been developed as supports for catalytically active components like precious metals or as catalyst themselves. In an aluminum microstructure reactor the walls of the micro channels of one passage was successfully coated with a porous alumina layer by a modified anodic oxidation method. Moreover, microchannels of microstructure reactors were successfully coated with SiO2, Al2O3 and TiO2 by the sol–gel process. First promising results have been obtained from depositing oxide nanoparticles (ZnO, CuO and Al2O3) by washcoat or electrophoretic deposition methods.