The reaction mechanism of electroless metal deposition proceeding selectively on a ZnO thin film coated on a glass substrate was investigated by x-ray diffraction, x-ray photoelectron spectroscopy, and inductively coupled plasma measurements. The ZnO thin film was activated for electroless metal deposition just by immersion in 1.1 mM PdCl2 solution adjusted to pH 2.5. In this process, Pd(II) was selectively adsorbed on the ZnO thin film while simultaneously the ZnO underwent dissolution. The dissolution of ZnO thin film easily occurred on the (002) face with polarity. The strongly adsorbed Pd(II) was reduced to Pd(0) by a reducing agent in the electroless plating bath and this served as a catalyst center. As a result, metal layers were obtained selectively on the ZnO thin film in the electroless plating bath.