MIR studies carried out in the work have allowed to establish that the glasses of the systems studied show domain composition [L.L. Hench, R.J. Splinter, T.K. Greenlee, W.C. Allen, J. Biol. Res. Symp. 2 (1971) 117; L.L. Hench, R.J. Splinter, W.C. Allen, T.K. Greenlee, J. Biol. Res. 5 (1972) 117]. Domain structure is close to that of the corresponding crystalline phases. It has been shown that even small amount of aluminium in the glass (5 mol. % of AlPO4) significantly influences both, its texture (microscopic and EDX studies) and its structure (spectroscopic studies). 27Al NMR investigations have made it possible to establish unequivocally that aluminium occurs exclusively in tetrahedral coordination, i.e. it is involved in the formation of glass framework. Presence of aluminium results in significant changes in the [SiO4]4− and [PO4]3− tetrahedra environment which is reflected in 23Na, 31P and 29Si NMR spectra. Changes in the shapes and positions of the bands in the NMR spectra of glasses belonging to the NaCaPO4-AlPO4-SiO2 system confirm great influence of aluminium on silico-phosphate glasses structure.