Hydrothermal process has been applied for effective production of Hydrogen from biowastes. In this study hydrothermal process for production of valuable Hydroxylapatitefrom chicken manure containing phosphorus was focused on. Conditions of 400?C and 26 - 27 MPa with addition of 1 mmol Ca(OH)₂ were determined as the optimal by using O-phospho-DL-serine as a model compound. Afterwards, the real biowaste containing phosphorous, chicken manure was processed under the same conditions. Formation of a Hydroxylapatite; in the solid residue was confirmed from X-ray diffraction (XRD) patterns, after purification. It was found that 27.9% of P in the chicken manure was converted to Hydroxylapatite. With the use of acetic acid as a chemical purification medium, Hydroxylapatite was obtained.