Methanol oxidative dehydrogenation to formaldehyde over a Fe-Mo oxide catalyst was studied experimentally in a packed-bed membrane reactor (PBMR) as well as in a conventional fixed-bed reactor (FBR) under identical overall reaction conditions. Two configurations for PBMR were investigated, using either oxygen (PBMR-O) or methanol (PBMR-M) as permeate, and the other reactant flowing over the catalyst bed. The influence of temperature, reactant residence time, feed concentration and nitrogen diluent split were studied, in the FBR experiments, selectivity to formaldehyde increased for increasing feed concentration of methanol and decreased when oxygen concentration was increased. This behavior indicated that the relative reactor performance should be in the order PBMR-O > FBR > PBMR-M, and this was confirmed experimentally.