Chemistry Division, Argonne National Laboratory, 9700 S. Cass A venue, Argonne, Illinois 60439, U.S.A. E-mail: Ichen@anlchm.chm.anL gov Fax: (630)-252-9289 peak intensities and peak positions. Their results indicated that as the coordination number of the Ti site increases from 4 to 6, the pre-edge intensity decreases and the energy of the peak increases by approximately 0.9 eV for each additional coordinating oxygen atom, starting from around 4969.6 eV for the tetrahedral Ti site. In this paper, we present our recent XAFS study at the Ti K-edge on TiO2 nanoparticles of 19 ]~ diameter without and with ascorbic acid. Based on our experimental results, as well as the results by Farges et a1.(1997), surface distortion of the Ti sites in small nanoparticles and its implication to the surface binding and photocatalytic activities will be discussed.