BaCeO(3), one of the candidate materials for solid oxide fuel cell electrolyte, is a H(+)/O(2-) mixed ionic conductor. In this study, we measured AC impedance of the anode with the O(2-), H(+) and O(2-), or H(+) as ionic charge carrier in the electrolyte. The measured impedance was analyzed by using the equivalent circuit, and the anodic reaction mechanism was analyzed by comparing the results and abstracted information in each system, in order to clarify the elementary reaction processes dominating the anodic reaction. The anodic reaction for H(+)/O(2-) mixed ionic conductor electrolyte is more complex than that for electrolytes with a single ionic charge carrier. Therefore, designing an electrode with lower overpotential requires the several elementary processes involved to be accelerated at the same time. A guideline for design of a lower overpotential electrode was proposed based on the knowledge acquired so far.