Charge transfer in Au nanoparticles (NPs) and Au@Ag core-shell NPs synthesized with a wet-chemical reduction method was investigated by X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) techniques. The electron depletion of Au 5d state in the Au@Ag x NPs compared to Au NPs was ascertained by the XANES analysis in Au L 2,3-edges though the Ag thickness (x nm), which affected the hole density of Au 5d states. The order of Au 5d-state hole density was confirmed as Au foil ≅ Au NPs < Au@Ag x NPs. The positive and negative shifts in the Au 4f and Ag 3d binding energies in XPS spectra of Au@Ag x NPs compared to Au or Ag NPs suggested that the Ag shell formation strongly contributes to the electron depletion of 5d state in Au atoms of the Au core. According to these results, we concluded that the electron transfer from Au to Ag in the Au@Ag heteromeric NPs followed the charge compensation mechanism.