Abstract The properties and structure of (45− x)Na 2O– xBaO–5ZnO–50P 2O 5 (0≤ x≤45 mol%) glasses were investigated. These properties include density, molar volume and glass transition temperature. The increase of density of glasses with increasing BaO content can be interpreted by differences of masses. The variation in the molar volume of these glasses is small. The glass transition temperature increases as the BaO is substituted for Na 2O. This behavior indicates that the replacement of Na 2O by BaO improves the strength of the cross-links between the phosphate chains of the glasses. The analysis of the infrared spectra of the studied glasses reveals that the increase of BaO content decreases the formation of end groups [(PO 3) n] n− .