We studied the reaction of methanol steam reforming in microchannel microreactors and elucidating the effect of catalyst structure and microreactor design on the reaction rate constant of methanol steam reforming. Three types of microreactors were studied-rectangular, cylindrical and tubular with fixed catalyst bed. To analyze the experimental data we used a simple kinetic model with power-law rate equation with the first reaction order for the methanol. It was shown that the value of reaction rate constant and hydrogen production depends on structure of the catalyst loaded into the reaction volume. The highest reaction rate constant and specific hydrogen production equal 8.11/(h g(cat)) was observed for the rectangular microreactor, with two metal plates with deposited catalyst. The cylindrical microreactors produced 6.21/(h g(cat)) of hydrogen. The tubular microreactor exhibited the lowest reaction rate constant and specific hydrogen production equal 4.91/(h g(cat)). This fact seems to be associated with the temperature gradient in the reactor due to the endothermic reaction of the methanol steam reforming. Using the Arrhenius equation the temperature gradient in the reaction volume was estimated-6.7 and 13.6K for the cylindrical and tubular microreactors, respectively. These results agreed with heat balance calculations. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.