An integrated microreactor system for the direct dehydrogenation of methanol to water-free formaldehyde was developed. The endothermic reaction can be homogeneously catalysed with evaporated sodium. At reaction temperatures of up to 1100 K nearly complete conversion of methanol can be achieved. Undesired consecutive reactions can be minimized, if the reaction products are rapidly cooled and if the residence time at reaction temperature is precisely controlled. Fast heating and cooling of the gases in the order of a few milliseconds is desired, specifications that can be met by microreactors. Several tests were carried out using conventional and microscaled systems. The results are compared and served as a base for the development of an integrated microsystem for the dehydrogenation of methanol. First, two different kind of mixers were tested. The results clearly showed that fast and homogeneous mixing of the gaseous sodium catalyst and the methanol is indispensable. Second, in order to improve the temperature profile in the reactor a cross flow micro heat exchanger was employed. A special adaptor with internal heater was developed, allowing to keep the gases at reaction temperature close up to the micro heat exchanger. The final setup allowed to obtain a formaldehyde selectivity of 80.3% at methanol conversion higher than 97%.