A series of phosphate based glasses of composition 45P2O5–(40−x)CaO–15Na2OxZnO (= 0, 3, 6, 8 10, and 12 mol%) were prepared employing melt-quenching techniques. Based on the thermal analysis data of glasses, the schedule of thermal treatments have been designed and employed to obtain their glass ceramic derivatives. The increase in thermal stability and decrease in crystallization tendency was observed from differential thermal analysis traces. The durability of phosphate glasses were improved as a result of the addition of ZnO content. The increasing ZnO content alters the phosphate glass structure and enhances the cross-link formation between different network chains. A broad-based characterization approach combining different techniques was used to investigate the in vitro properties of glasses and their glass-ceramic equivalents against the addition of ZnO content into the glass composition. The in vitro results revealed the decreasing nature of apatite forming ability of phosphate glasses with increase in ZnO content before and after thermal treatments. Both the glass and glass-ceramics containing ZnO content above 10 mol% exhibited poor in vitro performance mainly because of their dissolution nature. The weight loss analysis revealed that the decreasing solubility of glass and glass-ceramics was observed as increasing of ZnO content.