Nano-particles of hydroxyapatite (HAp) were prepared via an in-situ biomimetic process with polyacrylic acid (PAAc) as a host polymeric material. Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to test the physical and chemical characteristics of biocomposites. The formation of hydroxyapatite is confirmed by energy dispersive X-ray (EDX) spectroscopic analysis. Chemical binding between inorganic HAp and PAAc was investigated and discussed