Series of Ba/Sn phosphate glasses (33 and 40 mol% P2O5) are investigated by 31P MAS NMR and neutron diffraction to clarify the effects of substituting Sn with Ba. The structural parameters are related to glass properties, among them to the photoelastic constant (PEC). Different from the increase of the Sn−O coordination number to four in Zn/Sn phosphate glasses (33 mol% P2O5) the NSnOs of 3.2 and 3.4 do not change with substituting Sn with Ba. The stacking of layer-like entities of Sn or Ba oxygen polyhedra is suggested to cause the first scattering peak at 12 nm−1. Non-bridging oxygens shared by two or more Ba2+ lead to stiff networks with increasing BaO content which is accompanied with increasing Tg, decreasing thermal expansion, and better corrosion resistance. The slopes of the compositional dependence of the PEC of the Ba/Sn glasses are smaller than reported for Zn/Sn glasses which corresponds to the constant NSnOs.