Nanocrystals of titanium-substituted hydroxyapatite (CTHAp) were prepared with Ti4+ concentrations of x = 0, 0.1, 0.2 and 0.5 [x = Ti/(Ca + Ti)] at hydrothermal temperatures of 100, 150, 190 and 230 degrees C. The effects of reaction temperature and titanium concentration on the crystal were investigated by using TEM, XRD, FTIR, IP and XPS. The obtained CTHAp crystallites were rod like pure hydroxyapatite phase (about 70 nm in length and 10 nm in diameter), the crystallinity and grain sizes decreased with the increase of XTi, and increased with hydrothermal temperature from 100 to 230 degrees C. The concentration of Ti4+ near the surface is larger than in the bulk. The photocatalytic activity of CTHAp was examined by using decomposition of methylene blue (MB) and found that CTHAp had good photocatalytic activity under visible light and UV irradiation. (C) 2006 Elsevier B.V. All rights reserved.