Composite biomaterials based on calcium phosphate ceramic due to their high bioactivity are of interest for biological application and bone tissue repair. Structural and microstructural parameters of inorganic constituent of these materials are very important for the synthesis and characterization of composites. Quantitative and qualitative content, crystallite size of phases, as well as the degree of crystallinity have a great influence on the quality of composites, their application and bone tissue repair. X-ray diffractometry was employed to investigate the components of biocomposite materials, calcium phosphate (CaP) ceramic and poly-DL-lactide-coglycolide (DLPLG) polymer, as well as the biocomposite obtained from the mentioned components. Composite biomaterial was obtained by modified emulsion process. Using the Rietveld refinement, we analyzed CaP as an inorganic component of the composite, whence we have determined structural and microstructural properties of ceramic component of the investigated composite. The results obtained by structure refinement show that calcium phosphate ceramic materials synthesized at room temperature contain hydroxyapatite HAp as a predominant phase. The calculated Ca/P ratio is 1.667. The Rietveld analysis revealed lattice parameters a(angstrom)=9.4324(7) and c(angstrom)=6.8785(6) that are in agreement with the theoretical values.