Hydroxyapatite synthesized by a co-precipitation process of calcium nitrate and orthophosphoric acid was subjected to microwave irradiation at various powers until the precipitate dried. The particle size, as characterized by X-ray powder diffraction and transmission electron microscopy, was of nanodimensions. The results show the variation of particle size with the power of microwave irradiation. The shape of the particles also changed from needle-like to acicular to platelet form with the increase in microwave power. © 2006 Acta Materialia Inc.