Abstract: The hydrothermal synthesis of hydroxyapatite whiskers (HA_W) and the slurry-and-powder-metallurgy preparation of the hydroxyapatite whisker reinforced magnesium matrix composite (HA_W/Mg) were described. The structures and the associated properties of HA_W and HA_W/Mg composites were characterized by XRD, FTIR, FESEM and TG. The relationship between urea content and crystal structure of HA_W was explored. The thermal stability and microstructure of HA_W/Mg composites were investigated. The results show that pure carbonate-containing HA_W with belt-like morphology are acquired in this study; that the length and crystallinity of HA increase with the increase of urea content; that no chemical reaction occurs between HA_W and Mg under 600 ℃ and oxidation of Mg is not deteriorated by HA; that HA_W with high toughness distribute evenly in HA_W/Mg composites.