Abstract: A compact plate-fin reactor consisting of closely spaced plate-fins, where endothermic and exothermic reactions took place in alternate chambers was studied.In the reactor the catalytic combustion of reforming gas that was used to simulate the fuel cell anode off gas (AOG) supplied the necessary heat for the reforming reaction.Hydrogen was produced in one reforming chamber.Two vaporization chambers and two combustion chambers were integrated in one unit of the reactor.The reactor was compact,facilitating mounting and scale up.The effects of the ratio of water/methanol on the reactor performance were investigated, and the distribution of temperature in different chambers was studied.Besides, the steady-state behavior of the plate-fin reactor was studied.Internal plate-fins and [JP2]external catalytic combustion were applied to enhance the heat transfer in the reactor, which ensured both high methanol conversion and low CO concentration.In addition, this fully integrated reactor showed good testing stability.