A disk-type SM0.4Ba0.6Co0.2Fe0.8O3 (- delta) perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO + H-2). The reaction was carried out using Rh (1 wt%)/MgO catalyst by feeding CH4 diluted with Ar. While CH4 conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH4 conversion (90 %) and a high selectivity to CO (98 %) were observed at 1173 K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH4 compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH4 was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H-2 was fed. It is implied that the oxidation of CO and H-2 with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO2 and H2O react with CH4 by reforming reactions to form syngas. (c) 2005 Elsevier B.V. All rights reserved.