A sub-millimeter scale catalytic combustor was fabricated. Platinum catalyst coated on a porous ceramics support was placed in the combustion chamber. The chamber, sized 10 x 10 x 1.5 mm was covered with a GaAs window which is transparent to infrared radiation. The conversion rate was measured using gas chromatography. The temperature distribution in the combustion chamber was measured with an infrared thermal imager. The activated region where the catalytic reaction was violent was formed in the vicinity of the inlet. More than 95% of supplied gas reacted in spite of a small chamber space. The area of activated region increased with increased volume flow rate and decreased equivalence ratio. The concentration of platinum catalyst did not affect the reaction. A large content of heat generation and a broad activated region prevented reaction termination by soaked liquid water. The results of this work are important design factors for the development of an effective micro-catalytic combustor. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.