Hydroxyapatite (HA) has been widely investigated as bone substitute and/or bone defect repairing material. Many methods to synthesize nano-sized and weak agglomerated HA powders have been developed. However, no method has a satisfactory balance between the powder quality and the production cost. In this study, a simple, cheap and efficient process to prepare nano-sized and weakly agglomerated HA powder was developed, in which ultrasonication and a polymer dispersant of PEG were employed. The synthesized powders were characterized with XRD, TEM, and BET specific surface area analyzer. The results showed that the cooperation of ultrasonication and polymer dispersant greatly weakened the agglomeration in the HA powders, but ultrasonication alone did not influence the agglomeration observably. (c) 2005 Springer Science + Business Media, Inc.