The effect of surface modification with 3-aminopropyltriethoxysilane (APTES) and n-propyltriethoxysilane (PTES) on photo-catalytic activity and UV-shielding ability of fine TiO2 particles were investigated. The number of surface groups (N-R) [nm(-2)] which shows the density of modifier on TiO2 surface was calculated from the results of elemental analysis and BET measurement. The modified samples of which N-R are different were obtained by changing the concentration of modifier. When the photo-catalytic activity and UV-shielding ability of modified samples were evaluated, it was found that APTES was more effective modifier than PTES to obtained samples with low photo-catalytic activity and high UV-shielding ability. This is probably because the adsorption mechanisms on TiO2 surface between modifiers were different and N-R is a key factor to control the performances of fine TiO2 particles. The result of zeta potential showed that surface character of modified samples was varied by changing N-R. It suggested from these results that N-R affected the photo-catalytic activity and UV-shielding ability because N-R changed surface character of modified samples. (c) 2007 Elsevier B.V. All rights reserved.