It has been reported that the direct dimethyl ether fuel cell (DDFC) that uses the Pt-Ru catalyst on the anode has a lower performance than that using the Pt catalyst on the anode at ordinary temperature and pressure. We investigated the performance of the DDFC in detail using a cell equipped with a reference electrode. The anode performance of the Pt-Ru catalyst was higher than that of the Pt catalyst at current densities lower than 100 mA/cm(2) and was affected by the steam in the low potential region. The performance of the cell was improved with the anode bubbler and increased temperature. Moreover, it has been understood that an increase in the water content does not lower the resistance of the cell, but reduces the resistance by the reaction process based on the result of the impedance measurement. (c) 2006 Elsevier B.V. All fights reserved.