A microreactor for high temperature catalytic reaction was designed and fabricated using thin aluminium plates. A microreactor module consists of a parallel array of ten microreactor units, each made of two aluminium plates (Plate-A, Plate-B) connected in series and having ten microchannels. Leakage, pressure drop, and gas velocity of the reactor were measured. In order to perform forced composition cycling of partial oxidation of hydrocarbons, the pulse response method was employed to estimate the flow condition in the microreactor. At 773 K, where the catalytic reaction occurs, the reactor became highly airtight by thermal expansion and diffusion welding of the aluminium plates. The leakage was only 0.006-0.008% of the total flow rate. and the pressure drop of the reactor increased in proportion to the increase of the total flow rate in accordance with Fanning's equation. Additionally, the RTD curve of the microreactor module was calculated from the pulse response results. It was concluded from the results of the mean residence time, variance and standard deviation obtained from the curve that forced composition cycling could be performed within the period of 2-5 s. Moreover, the gas seems to flow equally to all the channels and units through by-passing flow or stagnation by deformation of the micro-channel during pressurization and heating were not observed.