Temporary bone replacement materials on the basis of calcium phosphates and hydroxyapatite (HAP) are used in surgery for filling bone defects. Components which are able to control the nucleation and crystal growth of HAP through their functional groups and which can additionally activate bone cells may be helpful in the development of materials with enhanced remodelling in vivo. In this study, the influence of O-phospho-L-serine (PS) on the materials properties of calcium phosphate bone cement composites was investigated. For up to an addition of 25 mg/g PS a strong increase in the stability of the cements under load was determined. The material was studied by scanning electron microscopy and transmission electron microscopy. A more dense microstructure and a plate-like morphology of the HAP-crystals were detected in the modified composites compared with the non-modified samples. By X-ray powder diffraction an inhibition of the dissolution of alpha-tricalcium phosphate (alpha-TCP) and dicalciumphosphate anhydrous (DCPA) particles was found. alpha-TCP and DCPA are the main constituents of the cement precursor. The results of cell culture studies using rat calvaria osteoblasts demonstrate a good viability of the cells on the PS-modified material. Furthermore, the proliferation and differentiation were found to be enhanced on the PS-modified material.