In this study, a single-stage, non-catalytic, dry methane plasmalysis process for producing mainly hydrogen and carbon powders using an atmospheric-pressure microwave plasma reactor is demonstrated. A high selectivity of H(2) and carbon powders (C(1)), and a low required energy consumption of H(2) could be obtained simultaneously at a low-applied power and a high inlet concentration of CH(4) ([CH(4)](in)), reaching 86.0% (selectivity of H(2)), 50.7% (selectivity of C(1)), and 6.7 eWmolecule-H(2), respectively, at 0.8 kW, [CH(4)](in) = 20%, and 12 slpm when CH(4) gas was fed from the downstream of the cavity resonator. In addition, large amounts of nano carbon powders, which consisted of C atoms and had a graphite-rhombohedral structure with a particle size of about 50 nm, were produced. These particles had potential for using as a support for platinum catalysts in fuel cells. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.