The present research work reports a low temperature (40oC) chemical precipitation technique for synthesizing hydroxyapatite (HAp) nanoparticles of spherical morphology through a simple reaction of calcium nitrate tetrahydrate and di-ammonium hydrogen phosphate at pH 11. The crystallinity of the singlephase nanoparticles could be improved by calcinating at 600oC in air. Thermogravimetric and differential thermal analysis (TG-DTA) revealed the synthesized HAp is stable up to 1200oC. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies confirmed the formation of spherical nanoparticles with average size of 23.15+-2.56 nm and Ca/P ratio of 1.70. Brunauer-Emmett-Teller (BET) isotherm of the nanoparticles revealed their porous structure with average pore size of about 24.47 nm and average surface area of 78.4 m2g-1. Fourier transform infrared spectroscopy (FTIR) was used to confirm the formation of PO, OH, CO chemical bonds. Cytotoxicity and MTT assay on MG63 osteogenic cell lines revealed nontoxic bioactive nature of the synthesized HAp nanoparticles.