A novel "sandwich" microreactor designed as a thin (similar to 300 mu m) porous plate of sintered metal fibers (SMF), sandwiched between metallic plates is reported. The SMF surface was coated by Fe-ZSM-5 thin film (< 2 mu m) rendering a catalyst highly active in the decomposition of N2O. The 3D open microstructure of SMF plates presents a low pressure drop during the passage of reacting gases. The high thermoconductivity of metallic SMF improves the heat transfer, avoiding hot-spot formation during exothermic reactions. The temperature measured in the middle and at the outlet of the reactor confirmed the isothermal reactor operation. The sandwich microreactor showed high permeability and a narrow residence time distribution close to an ideal plug-flow reactor. The kinetics of the N2O decomposition was studied and the reaction was shown not to be limited by mass transfer when conducted in the rnicroreactor.