The activity and selectivity of a palladium catalyst for the partial oxidation of methane have been improved by attaching two palladium catalysts to the faces of a zirconia-based ceramic and by applying an ac voltage between the two catalysts. Experiments were conducted between 873 and 1273 K with a mixture of 6.6% methane and 3.3% oxygen in argon. AC voltages at a frequency of 60 Hz were applied to the reactor. Above 1073 K, the amounts of unreacted methane and oxygen decreased, and the yields of hydrogen and carbon monoxide (synthesis gas) increased. At an ac voltage of 3 V at 1273 K, the yield of synthesis gas was up to two times more than that under the open-circuit condition. This enhancement was better than that found by applying a de voltage of 3 V, in which case the yield of synthesis gas was 1.3 times more than that under the open-circuit condition.