Low temperature (<500 K) methane steam reforming in an electric field was investigated over various catalysts. To elucidate the factors governing catalytic activity, activity tests and various characterization methods were conducted over various oxides including CeO₂, Nb₂O₅, and Ta₂O₅ as supports. Activities of Pd catalysts loaded on these oxides showed the order of CeO₂ > Nb₂O₅ > Ta₂O_5. Surface proton conductivity has a key role for the activation of methane in an electric field. Proton hopping ability on the oxide surface was estimated using electrochemical impedance measurements. Proton transport ability on the oxide surface at 473 K was in the order of CeO₂ > Nb₂O₅ > Ta₂O_5. The OH group amounts on the oxide surface were evaluated by measuring pyridine adsorption with and without H₂O pretreatment. Results indicate that the surface OH group concentrations on the oxide surface were in the order of CeO₂ > Nb₂O₅ > Ta₂O_5. These results demonstrate that the surface concentrations of OH groups are related to the proton hopping ability on the oxide surface. The concentrations reflect the catalytic activity of low-temperature methane steam reforming in the electric field.