We report the synthesis of a reduced Preyssler-type polyoxometalate (POM), using Ag-containing POM. Both parent and reduced clusters were obtained in the monocrystalline form, allowing structure determination by single-crystal X-ray diffraction. Furthermore, X-ray photoelectron spectroscopy, cyclic voltammetry, and magnetic susceptibility measurements suggested that the reduced cluster exhibits a valence of -23 and the Ag present in the reduced POM exists in a neutral state.