The purpose of the study was to prepare atmospheric pure-steam plasma using a microwave discharge and to apply the plasma to the reforming of hydrocarbon for hydrogen production. The experiment was conducted with 2.45-GHz microwave power supply with a special wave-guide designed elsewhere. The results showed that the pure steam plasma could be stably sustained, and analysis of emission spectra indicated that O, H and OH existed in the plasma. Hexane, as a model of gasoline, was used for the hydrocarbon reforming experiment. The results showed that H-2 and CO were predominantly produced, as suggested from equilibrium calculations, and that reforming could be accomplished. The conversion of hexane and steam was affected by the plasma power, and the ratio and total flow rate of the reactants. A fuel-cell power system including the steam plasma reformer was evaluated from experimental data and the results suggested that improvements are required for practical use of the plasma reforming method. (C) 2003 Elsevier Science B.V. All rights reserved.