The thermal degradation of the polyoxometallate Ba2H[alpha-FeO4W12O36] . 26H(2)O was investigated by means of X-ray heating patterns, thermal analysis (TG, DTG, DTA, DSC) and spectroscopic methods (IR, ESR, Mossbauer). The formation of the new hexagonal phase Ba0.167Fe0.083WO3+0.29 (alpha = 7.320, c = 7.389 Angstrom A) can be observed. The phase is stable at room temperature. Its structure is related to hexagonal tungsten bronzes but differs from them due to the presence of oxygen in addition to barium and iron along the hexagonal channels. The high positive charge of the cations leads to the maximum contraction of the cell parameter c.