For the first time systematic studies of crystallization processes and their dependence on the system composition, crystallization time, temperature, heating rate in system Na2O-CaO-Nb2O5-P2O5 were performed. Crystallization was studied using complementary methods - DTA, XRD, SEM with SE, BSE and EDS detectors, etc. The thesis discusses the advantages and disadvantages of methods for studying the crystallization process and assesses the influence of different parameters on results. The optimal parameters for investigation of poorly crystalline substance by XRD have been determined, which have been tested on a variety of poorly crystalline materials. Particular attention is paid to the crystallization studies of composition 8N, because in previous studies it was found to be biocompatible. The sequence of crystallization products, crystallisation mechanism and qualitative composition of crystalline products as well as morphology dependence on time, crystallinity and heating rate were studied. The microhardness, chemical resistance, solubility, dissolution kinetics and biological properties were determined for both glass and glass-ceramics with variable crystallite size. The results show that 8N with various degrees of crystallinity are promising biomaterials. In larger Na2O-CaO-Nb2O5-P2O5 system region changes in crystallization processes with variation of composition were analysed. The qualitative compositions of crystalline products obtained in slow cooling and reheating were compared. The glass forming region of system 8Na2O-CaO-Nb2O5-P2O5 was determined and role of niobium glass structure with the change of glass colour was analysed. The qualitative composition of the crystalline product and the parent glass composition were compared.