The mechanism of ruthenium dissolution in Direct Methanol Fuel Cell (DMFC) Membrane-Electrode-Assemblies (MEAs) was investigated by preparing various MEAs and subjecting them to continuous operation for a period of 250 hours. All of the MEAs exhibited voltage decay. The voltage decay for MEAs operating at 40 °C, 0.5 M methanol was in the range of 6 to 48 mV at an applied current of 50-mA/cm 2 and 67 to 150 mV at an applied current of 100-mA/cm 2. The technique of anode polarization was used to determine the source of degradation and revealed that anode performance in these MEAs was constant and that the cathode was more sensitive to duration operation. EDAX analysis was performed on each cell to determine if ruthenium had dissolved from the anode and precipitated onto the cathode, no ruthenium was found on the MEA. This paper discusses stack properties that can promote ruthenium dissolution in DMFC MEAs. copyright The Electrochemical Society.