Vacancy ordered maghemite (gamma-Fe2O3) nanoparticles functionalized with nanohydroxyapatite (HAp - Ca-10 (PO4)(6)(OH)(2)) have been successfully synthesized using an inexpensive co-precipitation chemical route. Evidence for the presence of vacancy order in maghemite was shown by the superstructure lines observed in X-ray diffraction. The adsorption of carboxyl groups of citric acid (C6H8O7) onto gamma-Fe2O3 nanoparticles was investigated by FTIR, XPS and Mossbauer spectroscopy. From XPS surface analysis, two binding energies related to oxygen were attributed to bindings between C6H8O7/gamma-Fe2O3 and C6H8O7/HAp from an interfacial reaction promoted by strongly adsorbed H2O molecules at the surface of these nanomaterials. Le Bail refinement of the XRD patterns showed the formation of well-crystallized pure tetragonal maghemite before and after functionalization with nanoHAp. The temperature dependence of hyperfine parameters of pure and functionalized gamma-Fe2O3 nanoparticles was investigated via Mossbauer spectroscopy. TEM revealed the formation of quasi-spherical gamma-Fe2O3 nanoparticles with an average diameter of ca. 12 nm and 16 nm before and after functionalization with nanoHAp in agreement with Le Bail refinement. Magnetometry measurements showed a saturation magnetization of 12 emu/g and a blocking temperature of 340 K for the functionalized gamma-Fe2O3 nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.