The full details of synthesis and characterization of diiron(III)-substituted gamma-Keggin silicotungstate, [gamma(1,2)-SiW10{Fe(OH2)}(2)O-38](6-) (abbreviated as I) were reported. This complex was synthesized by the reaction of the lacunary [gamma-SiW10O36](8-) With Fe(NO3)(3) in an acidic aqueous solution and isolated as the tetra-n-butylammonium salt (TBA-I). TEA-I has been characterized by infrared, Raman, W-183 NMR, W-visible, Mossbauer, and ESR spectroscopy, TG/DTA, FAB-mass, and magnetic susceptibility measurements, elemental analysis, and acid/base titration. The W-183 NMR, infrared, Raman, and UV-visible spectroscopy indicated that I has a gamma-Keggin structure with C-2v symmetry. It was shown by the magnetic susceptibility measurement and Mossbauer, ESR, and UV-visible spectroscopy that I shows an antiferromagnetic coupling of the two high-spin Fe3+ centers.