We investigated the composition, morphology, and dissolution behavior of an Au-Ag nanoporous structure formed by electrodeposition and dealloying. Formation of the films was carried out by changing the bath composition and the annealing temperature. The amount of Ag decreased from 70 wt. % to 45-50 wt. % after dealloying. As seen from analysis by a glow discharge optical emission spectrometer (GDOES), not only the amount of Ag, but also that of Au was decreased after dealloying, and a highly concentrated Ag layer was generated at the surface. When the Ag dissolves, an underpotential deposition (UPD) might be introduced, followed by the generation of a high concentration of Ag. From the anodic polarization measurement, the anodic current densities of the samples under 1.5 V were larger than those of the samples under 1.0 V, resulting in the generation of many nanopores. It was confirmed that dealloying involved three processes: whole film dissolution (includes Au dissolution), defects dissolution at the grain boundary, and Ag-selective dissolution.