Abstract 57Fe Mössbauer spectra of xNa 2O · (99 − x)WO 3 · 57Fe 2O 3 glasses (30 ≤ x ≤ 42) comprised of a doublet due to octahedral iron, Fe 3+(O h), and a weak doublet due to Fe 2+(O h); a large Debye temperature of 580 K was obtained at low temperatures. Fourier transform infrared spectra of the sodium tungstate glasses showed a gradual increase in the fraction of WO 4 tetrahedra (T d) when Na 2O content was increased. Mössbauer spectra of the tungstate glasses irradiated with 60Co γ-rays showed an increase in the fraction of Fe 2+, due to electron transfer (scattering) from WO and FeO bonds to Fe 3+, as the electron spin resonance spectra of iron-free sodium tungstate glass indicated a simultaneous formation of W 5+ and the ‘hole’ trapped on the oxygen atom. From the linear relationship between glass transition temperature, T g, and quadrupole splitting, Δ, of Fe 3+ (‘ T g − Δ rule’), the slope of the straight line was estimated to be 260°C/(mm s −1). Mössbauer spectra of heat-treated tungstate glasses showed a gradual change from Fe 3+(O h) to Fe 3+(T d), along with the precipitation of the Na 2W 2O 7 phase composed of W 6+(O h) and W 6+(T d). These results indicate that iron occupies W 6+(O h) sites in glasses, while it occupies W 6+(T d) sites in glass-ceramics.