Hydroxyapatite (Ca-10(PO4)(6)(OH)(2):HA) with highly designed microstructures is required for bone filling materials and tissue engineering of cultured bones. This study deals with the shape control of HA particles and preparation of HA sheet from fibrous HA. Fibrous particles of HA with the aspect ratio of about 60 were prepared hydrothermally at 150 degreesC from the mixed solution of calcium acetate and phosphoric acid. The aspect ratio of the fibrous particles depended on the concentration and the value of Ca/P ratio of the mixed solution. The HA sheet must be a biostable material according to the soaking test with simulated body fluid.