A facile template-free sonochemistry-assisted microwave method was successfully developed for the synthesis of mesoporous hydroxyapatite nanoparticles (MHN) in a short time. The prepared MHN were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and N-2 adsorption-desorption isotherms. TEM images showed a clear rod-like morphology with length of 50-100 nm and width of about 20 nm. XRD and FTIR indicated a typical hydroxyapatite phase with high crystallinity. N-2 adsorption-desorption isotherms revealed an irregular mesoporous structure. Judging from the values calculated from N-2 isotherms, the specific surface area and pore volume obviously decreased after the sintering process. In a typical example, the specific surface area, pore volume, and pore size of MHN before and after calcination were 79.74 m(2)/g, 0.46 cm(3)/g, 2.7 nm and 45.41 m(2)/g, 0.22 cm(3)/g, 2.8 nm, respectively. In addition, MHN could be synthesized in a period of time as short as 10 min. Further investigation indicated that microwave radiation played a dominant role in the emergence of mesoporous structure, while ultrasound irradiation acted as a supporting role. Based on the above results, a possible mechanism of formation of mesoporous hydroxyapatite has been proposed.