Single-phase calcium hydroxyapatite (HAP) was synthesized by a sol–gel route using calcium nitrate solution and ammonium dihydrogen phosphate solution as Ca and P sources and alginic acid as a chelating agent. The dried gel was heat-treated at different temperatures in the range of 110°–900°C. Structural evolution from sol to gel and from the gel to HAP was studied by the powder X-ray diffraction method, Infrared spectroscopy, and thermal analyses. The formation temperature of HAP was confirmed to be ∼300°C. Examination of the product obtained at 300°C under TEM suggested the development of hexagonal-shaped nanoparticles, with the average particle size in the range of 50–100 nm.