Surface free energy is one of the parameters accompanying interfacial phenomena, occurring also in the biological systems. In this study the thin layer wicking method was used to determine surface free energy and its components for synthetic hydroxyapatite (HA) and natural one obtained from pig bones. The Raman, FTIR and X-Ray photoelectron spectroscopy, X-ray diffraction techniques and thermal analysis showed that both samples consist of carbonated hydroxyapatite without any organic components. Surface free energy and its apolar and polar components were found to be similar for both investigated samples and equalled gamma(TOT)(S)= 52.4 mJ/m(2), gamma(LW)(S)= 40.2 mJ/m(2) and gamma(AB)(S)= 12.3 mJ/m(2) for the synthetic HA and gamma(TOT)(s)= 54.6 mJ/m(2), gamma(LW)(S)= 40.3 mJ/m(2) and gamma(AB)(S)= 14.3 mJ/m(2) for the natural one. Both HA samples had different electron acceptor (gamma(+)(s)) and electron donor (gamma(-)(s)) parameters. The higher value of the electron acceptor was found for the natural HA whereas the electron donor one was higher for the synthetic HA. (C) 2017 Elsevier B.V. All rights reserved.