The FTIR, Raman, UV-Vis, P-31 MAS-NMR, DTA, and refractive index measurements have been combined to investigate a series of glasses with the general formula 20Na(2)O-5Al(2)O(3)-xTiO(2)-(45-x)Nb2O5-30P(2)O(5), 15 <= x <= 45. The glass structure, as well as thermal, optical, and chemical durability properties, were then described as functions of the f(Nb)/f(Ti) ratio. An increase of the f(Nb)/f(Ti) ratio correlates with a decrease in length of the average phosphate chains linked through Nb-O-P and Ti-O-P bonds, with an increase in the glass stability and with increase in the linear refractive indices at 632.8 nm from 1.79 to 1.89. Furthermore, niobium is more effective than titanium in improving chemical durability.