This article describes a material prepared for biocements for medical use in human body. Biocements are used, for example, for bone implants or as a filling of bone cavities. The main method of preparation of Si3N4 microspheres in this article is based on flame synthesis. Different compositions of Si3N4 and Ca3(PO4)2 powder mixtures were prepared and synthesized in CH4 + O2 flame. The aim was to characterize the influence of the proportion of Si3N4 and Ca3(PO4)2 and the preparation of microspheres on their resulting chemical and crystalline phase composition and to determine the effect of these changes on the biological characteristics of the obtained microspheres.