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 degrees-900 degrees 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 similar to 300 degrees C. Examination of the product obtained at 300 degrees C under TEM suggested the development of hexagonal-shaped nanoparticles, with the average particle size in the range of 50-100 nm.