Highly active and coke-resistant Rh catalysts were developed for methane steam reforming in microchannel chemical reactors. Rh loading was optimized on a stable MgO-Al2O3 support to improve the volumetric productivity for methane conversion. Catalyst activities were stable over a wide range of steam/carbon ratios. In particular, experimental results demonstrated that Rh/MgO-Al2O3 catalysts are extremely active for methane steam reforming and are resistant to coke formation at stoichiometric steam/carbon ratio of 1 for over 14 h time-on-stream with no sign of deactivation. Methane steam reforming activities on this catalyst is compared in both a microchannel reactor and a conventional micro-tubular reactor. Significant performance enhancement was observed in microchannel reactors owing to improved heat and mass transfer. (C) 2004 Published by Elsevier B.V.