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.