A new phenyltin tungstosilicate derivative, [(PhSnOH(2))(2)(gamma-SiW10O36)(2)](10-) (1), has been prepared by reaction of phenyltin trichloride with K-8[gamma-SiW10O36]. xH(2)O. The new heteropolyanion was characterized by elemental analysis, infrared spectroscopy, multinuclear NMR, and X-ray crystallography. The crystals of Cs9H[(PhSnOH(2))(2)(gamma-SiW10O36)(2)]. 16H(2)O (Cs Salt of 1) are triclinic, space group P (1) over bar, with lattice constants a = 12.401(3) Angstrom, b = 13.832(3) Angstrom, c = 16.313(3) Angstrom, alpha = 96.17(2)degrees, beta = 109.73(2)degrees, gamma = 97.13(2)degrees, V = 2579.9(10) Angstrom, and Z = 1. Anion 1 has a structure of virtual C-2h symmetry With two phenyltin groups sandwiched between two gamma-SiW10 groups. Such a structure is different from all previously reported polytungstates derived from [gamma-SiW10O36](8-) lacunary anions.