Ternary systems based on hydroxyl apatite-purified montmorillonite-organic polymer were synthesized in situ in hydrothermal conditions at high pressures and low temperatures. Complex nanostructured materials were obtained. The possibility of the formation of strong chemical bonds under high pressures, between organic-inorganic phases, has been investigated by Fourier Transform Infrared Spectroscopy (FT-IR). Microstructure and morphology have been investigated by High Resolution Transmission Electron Microscopy (HRTEM). Studies to understand the influence of the synthesis conditions on the final form of nanocomposite have been performed.