In order to enhance the long-term performance of DMFC, new processing of MEA was attempted. Heat treatment of MEA at 130℃ could produce higher proton conductivity of Nafion binder due to the ionic cluster formation and less dissolution in 2M methanol solution due to the increase of crystallinity of Nafion binder. Thus it was found that the heat treatment of MEA could improve the stability at the interface of the membrane/electrode and catalyst/binder, leading to the higher performance and long-term stability of the MEA. In this study, the decay rate of ammealed MEA is about 4.8 μW/hr, therefore, 3,000hrs operation of DMFC is expected above 80% of initial performance. This is a very surprising improvement in long-term performance of DMFC with simple technique.