By the reaction of TBA₄H₄[γ-SiW₁₀O₃₆] (TBA = tetra-n-butylammonium) with AgOAc (OAc = acetate) using dimethylphenylsilane as a reductant in acetone, a unique polyoxometalate containing a discrete octahedrally shaped [Ag₆]⁴⁺ cluster, TBA₈[Ag₆(γ-H₂SiW₁₀O₃₆)₂]·5H₂O, could be synthesized, and the molecular structure was determined.