In this study, hydroxyapatite (denoted as HAp) nanostructure with uniform morphologies, controllable size, nano-dispersion and narrow size distribution in diameter has been synthesized successfully by low-temperature hydrothermal process, and the as-synthesized powders were characterized by XRD, scanning electron microscopy, high-resolution transmission microscopy, FT-IR, Zetasizer and inductively coupled plasma. In the present work, a novel sonochemical technique using CaHPO₄2H₂O/NaOH/distilled water with cetyltrimethylammonium bromide ((CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻) designated as CTAB) under a hydrothermal condition to synthesize HAp nanostructure was described. Furthermore, the usage of a high basic condition and a water environment are the two crucial keys in ensuring the formation of HAp in the hydrothermal/sonochemical processes. However, the crystallite size and crystallinity degree of the HAp increased with increasing annealing temperature. Indeed, the present work will introduce a new method in synthesizing HAs for scientific and medical engineering.