When compacts of the TiO2 powders having high photocatalytic activities were fight-illuminated beforehand in simulated body fluid (SBF) from an Hg lamp and subsequently held at 37degreesC, bonelike apatite crystals were formed on the surfaces. Color of the compacts was turned into bluey violet by the illumination, showing generation of Ti3+ and negative charging of the surface. X-ray photoelectron spectroscopic analysis showed that basic Ti-OH groups, which induce the apatite nucleation, is formed abundantly at the negatively charged surface of TiO2 by the light-illumination in SBF. This finding indicates that we are able to prepare novel bioactive materials controlled by photoexcitation of TiO2. (C) 2002 Elsevier Science B.V. All rights reserved.