Mössbauer measurements of sodium borate glasses 4 Fe₂O₃· x Na₂O· (96-x) B₂O₃ (x=6, 10, 15, 20, 25, 30) have been carried out. It was found that Fe³⁺ is present in both octahedral and tetrahedral sites, whereby the tetrahedral sites are preferred. In the range of Na₂O contents higher than about 15 mol%, the isomer shifts and quadrupole splittings for Fe³⁺ decrease continuously with increasing Na₂O concentration. These changes could be attributed to the formation of non-bridging oxygens (NBO) in the neighborhood of ferric ions. Increasing Na₂O content thus gives rise to more NBO increasing the symmetry of the iron polyhedra.