Synthetic hydroxyapatite (HA) has been extensively used as an implant material owing to its excellent osteoconductive properties. The preparation of nanocrystalline HA is of paramount importance as the large surface area of the diminutive crystals makes them very active and consequently strongly affects the properties of it. In this paper, to study the effect of microwave irradiation power and time, nanocrystalline HA was synthesised at different microwave irradiation times (15, 45, 120, 240 and 600 min) and with different microwave powers (800 and 1100 W). This study also investigated the crystallisation of HA in the presence of sodium alginate and alginic acid at different addition levels (5, 10 and 15 wt-% to the final HA). It was found that crystallinity of the HA increases with increasing microwave irradiation time and/or power. Sodium alginate or alginic acid addition during crystallisation of HA decreases the crystal size and crystallinity of the precipitated HA. © 2010 W. S. Maney & Son Ltd.