The bioactive nanoparticles in the system CaO-P2O5-SiO2 were synthesized via microemulsions method in this study. The structure and properties of the nanoparticles were investigated in details using XRD, TEM, FTIR, BET techniques. It was found that, in a stable phase W/O emulsions, the diameter of the nanoparticles were related to the molar ratio of water to surfactant (γ). Under the favorable conditions, i.e. γ=6, nano-sized spherical amorphous particles could be obtained with the average diameter of 25 nm. The microemulsions could be an alternative method to prepare bioactive nanoparticles for bone reparation and bone tissue engineering scaffolds.