Bioactive glasses are known to quickly induce the formation of a calcium phosphate layer at their surface when in contact with biological fluids; this property is particularly interesting for clinical applications. Because the bioactivity process deeply depends on the glass composition and texture, and because little has been attempted in quantifying the reaction kinetics of these materials, we developed an unconventional methodology to highlight the influence of the phosphorus oxide content on the physicochemical properties of bioactive glasses. Sol-gel derived glasses in the SiO2-CaO and SiO2-CaO-P2O5 systems were soaked in biological fluids for varying periods. After immersion, the surface changes were characterized using particle-induced X-ray emission (PIXE) associated to Rutherford backscattering spectroscopy (RBS), which are efficient techniques for multielemental analysis. In addition, these ion beam methods permit accurate trace elements quantification. Chemical mapping of the glass/biological fluids interface at a micrometer scale reveals the bone-bonding ability of our materials. The formation of a Ca-P-Mg layer occurs after a few hours of interaction. The kinetics of the evolution of the calcium phosphate layer is estimated by modeling the Ca/P atomic ratio decrease at the glass surface, along with supersaturation studies in biological fluids. The materials composition and texture significantly affect the kinetics and amplitude of the bioactivity mechanism. Dealkalinization of the glass matrix and the first appearance of the calcium phosphate layer are delayed for SiO2-CaO-P2O5 glasses when compared to SiO2-CaO glass. evertheless, once the Ca-P-Mg layer formation has begun, the layer extends on greater depths and is more quickly changed into a bone-like apatitic phase for P-containing glasses. The presence of phosphorus in the primary glass matrix facilitates the transformation of the initially amorphous calcium phosphates into bone-like apatite crystals. Moreover greater quantities of magnesium are incorporated for SiO2-CaO-P2O5 glasses: this is important information for medical applications due to Mg bactericidal and anti-inflammatory properties.