The reaction mechanism of methane activation using non-equilibrium pulsed discharge was largely clarified from the emission spectroscopic study and experiments with higher hydrocarbons and some kinds of isotopes. The strong emission of atomic carbon and C-2 swan band system was observed as well as H Balmer series emission. This indicates that methane was highly dissociated into C and H by electron impact, which is consistent with the result of high C2D2 composition in produced acetylene when the mixture of CH4 and D-2, was fed into discharge region. High electron energy contributed to produce atomic carbon directly from methane, and high electron density promoted the dehydrogenation from CH3, CH2 and CH to produce atomic carbon consecutively. The reason for the high selectivity to C2H2 was the high concentration of CH or C-2 formed from atomic carbon, and the repetition mechanism of decomposition and recombination among C, CH, C-2 and C2H,. (C) 2003 Elsevier Ltd. All rights reserved.