Oxygen permeation and partial oxidation of methane (POM) were investigated in 75 wt.% Ce(0.85)Sm(0.15) O(1.925)-25 wt.% Sm(0.6)Sr(0.4)FeO(3-delta) (SDC-SSF) dual-phase composite membrane reactors. The dual-phase membrane prepared via a one-pot method comprises a fluorite-type oxide ionic conductor (SDC) for the transport of oxide ions and a perovskite-type mixed conductor (SSF) for the transport of both oxide ions and electrons. X-ray diffraction (XRD) results reveal good phase compatibility between the fluorite and perovskite oxides even after sintered at high temperature. The oxygen permeation flux increased with time in the initial stage, from 0.23 to 0.5 cm(3) cm(-2) min(-1) in the first 18 h. Once a steady state was reached, the permeation flux remained constant in the investigated period (> 500 h). Long-term operation of POM reaction was successfully achieved in dual-phase membrane reactors, and methane conversion and CO selectivity >98% were obtained for pure methane as the feed. XRD, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) characterizations reveal good structural stability for the dual-phase membrane, even after long-term operation under syngas production conditions. (C) 2010 Elsevier B.V. All rights reserved.