This paper reports the preparation, characterization and stability tests of Pd-based thin membranes for fluidized bed membrane reactor applications. Various thin membranes have been prepared by simultaneous Pd-Ag electroless plating. A simple technique for sealing of the produced membranes is reported and discussed. The membranes have been characterized for single gas permeation, and afterwards used for permeation of mixtures of gases and under fluidization conditions. The membranes have shown very high permeation rates and perm-selectivity when used as permeators. When applied in fluidized bed reactors it has been found that the membranes are stable as long as no interaction between the fluidization catalyst and the membrane surface occurs. For some catalysts a strong chemical interaction between the catalyst and the membrane surface has been observed which caused a drastic decrease in the membrane flux.