This article reports a novel and facile solid-based steam-assisted conversion method for the synthesis of hydroxyapatite (HAP, Ca-10(PO4)(6)(OH)(2)) nanorods and nanoparticles. After steam treatment at 180 A degrees C for 20 h, the wet solid of brushite (CaHPO4 center dot 2H(2)O), which was precipitated from reaction between calcium nitrate [Ca(NO3)(2)] and diammonium hydrogen phosphate [(NH4)(2)HPO4], was transformed to HAP nanorods with dimension of 100-300 nm in length and 56 +/- A 10 nm in diameter through a solid-gas reaction. By the same steam treatment, the dried brushite was converted to nanoparticles of HAP with small aspect ratio and particle size of 70 +/- A 18 nm. As compared with commercial HAP material, the nanostructured HAP materials exhibited superior sinterability in terms of density and hardness as well as excellent thermal stability. This simple, organic-free and cost-effective synthesis route with low reactant volume offers high potential for large-scale production of nanostructured HAP.