The devitrification phenomenon of CaO/P2O5 glass with TiO2, Al2O3, and SiO2 additions were investigated using thermal analysis techniques. To determine, whether, the devitrification begins at the surface or in the bulk of these glasses, we compared the peak temperatures of exothermic for coarse and fine particles. The devitrification mechanism of CaO/P2O5 glass will change by adding additives, such as TiO2, Al2O3, and SiO2. The addition of additives will induce the surface nucleation mechanism of these glasses, but the addition of additives, such as TiO2 and Al2O3 are found to promote volume nucleation when the amount of addition exceeds 5 and 10 mol%. respectively.