This paper describes extensive experimental research on steam reforming of methane using barrier discharges with/withoutNi/SiO2 catalyst. Nickel catalyst clearly showed chemical activity at 400degreesC in the presence of barrier discharge. Methane conversion largely exceeded over equilibrium conversion rate, whereas product selectivity tended to follow equilibrium composition at given temperature: energy cost and energy efficiency achieved 134 MJ/kg H, and 69%, respectively. Electric property was unchanged in the presence of nickel catalyst, but at least 400degreesC must be maintained in order to derive synergistic effect between barrier discharge and Ni/SiO2 catalyst. Methane activation mechanism is also discussed based on numerical simulation on streamer propagation in pure methane. Vibrationally excited methane is most abundant (1016 cm(-3) at 300 K, 101.3 kPa) and long-lived (similar to1 mus) radical species produced by electron impact, and those vibrational species seemed to improve dissociative chemisorption on nickel surface at low temperature, leading to remarkable process improvement. (C) 2003 Elsevier B.V. All rights reserved.