IN PRESENT study, Different bioactive glass samples are prepared based on the following general formula: [65%SiO2–(25-X) %CaO–10% P2O5–X%ZnO)]; Ca2+ is gradually substituted with Zn2+ (percentages of X= 0, 2, 4, 6, 8 and 10 mol %) by a quick alkali-mediated sol–gel method. Development of a calcium phosphate (CP) layer on their surfaces is studied by soaking them in a simulated body fluid (SBF) for different periods. The consequent formation of the CP layer is studied by means of appropriate techniques such as X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) with an energy dispersive system (EDXS). The concentration of Ca2+, P5+ ions released from the samples into the SBF is measured by using UV-Vis Spectrophotometer and biochemical Kits. The results show that the formation of calcium phosphate layer on glass surfaces is inhibited by ZnO substitution, and strongly dependent on Zn2+ concentration.