High-purity　anatase　TiO2　nanoparticles　were　prepared　using　a　low-temperature　sol-gel　route.　The　as-prepared　sample　was　characterized　by　X-ray　diffraction,　transmission　electron　microscopy,　infrared　spectroscopy,　thermogravimetric　analysis,　UV-vis　spectroscopy,　and　photoluminescence.　It　is　shown　that　the　as-prepared　sample　crystallized　in　a　pure　anatase　phase　with　an　average　crystallite　size　of　about　7　nm,　and　the　surfaces　were　highly　hydrated.　These　nanoparticles　were　stabilized　as　a　water　suspension　via　the　cooperation　of　DLVO　force　and　surface　hydration　force.　These　suspensions　showed　characteristic　band-gap　emission　at　397　±　1.5　 　nm,　which　is　a　little　red-shifted　compared　with　the　band-gap　energy　of　indirect　electronic　transition　measured　in　the　UV-vis　absorption　spectrum.　These　observations　were　explained　by　the　light-induced　relaxation　of　polar　water　molecules　in　the　surface　hydration　layer.　©　2007　Elsevier　Inc.　All　rights　reserved.