It was revealed that Cu-plated Nafion exhibits an extremely large bending upon applied voltage recently. Although this phenomenon has been thought to be owing to the continuous transport of hydrated Cu2+ through the ionization of Cu layer on Nafion surface, we reached the conclusion that it is primarily owing to the shift of a large amount of hydrated Cu2+ en masse, which were originally contained in Nafion body. Formation of another Ni metal layers on Nafion surfaces drastically improves the force Nafion generates. This is owing to the reinforcement of Nafion matrix. The force of Ni plated Nafion continues to increase with time upon applied voltage, altough it decays without nickel plating layers. Furthermore, it was found that Nafion bending curvature was sensitive to the applied load on it. It demands a detail investigation on Nafion for the purpose of achievement a practical Nafion actuator.