Hollow hydroxyapatite microspheres, consisting of a hollow core and a porous shell, were prepared by converting Li(2)O-CaO-B(2)O(3) glass microspheres in dilute phosphate solution at 37 degrees C. The results confirmed that Li(2)O-CaO-B(2)O(3) glass was transformed to hydroxyapatite without changing the external shape and dimension of the original glass object. Scanning electron microscopy images showed the shell wall of the microsphere was built from hydroxyapatite particles, and these particles spontaneously align with one another to form a porous sphere with an interior cavity. Increase in phosphate concentration resulted in an increase in the reaction rate, which in turn had an effect on shell wall structure of the hollow hydroxyapatite microsphere. For the Li(2)O-CaO-B(2)O(3) glass microspheres reacted in low-concentration K(2)HPO(4) solution, lower reaction rate and a multilayered microstructure were observed. On the other hand. the glass microspheres reacted in higher phosphate solution converted more rapidly and produced a single hydroxyapatite layer. Furthermore, the mechanism of forming hydroxyapatite hollow microsphere was described. (C) 2009 Elsevier Ltd. All rights reserved.