Abstract: Using simulated body fluid（SBF） as solvent，CaCl₂ and K₂HPO₄·3H₂O as raw materials，nano-sized spherical hy- droxyapatite（HA） powders have been synthesized in almost neutral solution at 37 ℃ without adjusting pH during the whole  reaction.The powders were characterized by XRD，FE-SEM，FT-IR，and TEM etc..Results showed that the synthesized powders were nano-sized spherical hydroxyapatite with diameters between 60~80 nm，and that the particle was composed of single-crystals with the diameter of about 15 nm.Moreover，the product did not need sintering treatment.The reaction time was very important during the whole process.The HA can be synthesized in 1 min with poor crystallinity，but crystallinity became better with the reaction time increasing to 6 h.

Key words: simulated body fluid, nano-sized hydroxyapatite, single-crystal