Effects of MgO doping on properties of P₂O₅–CaO–Na₂O glass system were investigated. The glass samples were prepared by conventional glass melting technique at 1000 °C for 1 h. Thermal parameter of each glass sample were studied by differential thermal analysis (DTA). The glass samples were annealed at crystallization temperature to form glass ceramics. The glass ceramics were investigated in terms of phase formations by XRD, microstructure by SEM and in vitro bioactivity. The phases formed in all glass ceramics are calcium phosphate (Ca₂P₂O₇file no. 09-0346), sodium phosphate (NaPO₃ file no. 11-0650) and sodium calcium phosphate (Na_1.8Ca_1.1P₆O₁₇ file no. 47-0863) as detected by XRD. The 5–10 mol% MgO glass ceramics having well separated two crystallization peaks (T_x1 and T_x2) within the temperature range of 557–590 °C contained additional sodium magnesium phosphate (NaMg(PO₃)₃ file no. 72-2341). Large porosity was found in all glass ceramics due to free volume and void formation during the crystallized phase. The in vitro study revealed that all glass ceramic samples exhibited apatite cell growth at the surface after immersed in simulated body fluid (SBF) for 7 days. The results suggested that these glass ceramics were appropriate for biomedical application.