Nanorod bundles of hydroxyapatite (nrHA) with ordered radiated structure was successfully prepared through hydrothermal treatment, with the hexadecyltrimethylammonium bromide (CTAB) and sodium citrate as surfactant and crystal modifier, respectively. The results showed that the citrate and CTAB played an important role in assembly of nanorods. Moreover, the pH value of the original solution also can influence the final morphology of products. The possible formation mechanism of nanorod bundle structure was discussed in detail. (C) 2013 Elsevier B.V. All rights reserved.