Calcium deficient hydroxyapatite (CDHA) nanoparticles with a Ca/P ratio of 1.6 were synthesized by accelerated sonochemical process. The synthesis was carried out using calcium nitrate and diammonium hydrogen phosphate in an ultrasonic bath operated at a fixed frequency of 135 kHz and 250 Watts power. The effect of ultrasonic radiation as a function of time over the formation and structure of nanoparticles were investigated using X-ray diffraction, spectroscopy and microscopy methods. The synthesized nanocrystals showed X-ray powder diffraction pattern corresponding to that of hydroxyapatite stoichiometry with CDHA characteristics. HPO2- 4 Fourier transform infrared vibration band observed at 875 cm-1. Transmission electron microscopic analysis confirmed the nanocrystalline nature and growth of acicular, rod and needle-like CDHA nanocrystals morphology with increasing irradiation time. © 2014 American Scientific Publishers. All rights reserved.