Size-controlled synthesis of hydroxyapatite nanorods were carried out by chemical precipitation method using polyethylene glycol (MW 600), Tween 20, trisodium citrate, and D-sorbitol as organic modifiers and starting from calcium nitrate, phosphoric acid, and ammonia solution. The influence of the organic modifiers on the sizes of the resultant HAP nanorods was investigated under different synthesis temperatures. It was found that polyethylene glycol was beneficial to the formation of HAP nanorods with a larger aspect ratio (average length/average diameter) at high synthesis temperature, Tween 20 and trisodium citrate favored the formation of small-sized HAP nanorods, and D-sorbitol helped the formation of HAP nanorods with long length at low synthesis temperatures. (c) 2006 Elsevier B.V. All rights reserved.