Bi2O3 surface-modified TiO2 nanoparticle has been synthesized by sol-hydrothermal processes, followed by post-treatment with an appropriate amount of bismuth nitrate solution, and also characterized by XRD, Raman, BET, TEM, FT-IR, XPS, UV-vis DRS and SPS techniques. The effects of the surface-modification with Bi2O3 on the thermal stability, photoinduced charge separation and photocatalytic activity for degrading rhodamine B (or phenol) under ultraviolet (or visible) irradiation are investigated in detail, along with their relationships and the activity enhancement mechanisms are also suggested. The results show that the modi. cation with Bi2O3 can improve the thermal stability of the as-prepared anatase crystallites, consequently enhancing the anatase crystallinity so as to promote the photoinduced charge separation. And the modi. cation with Bi2O3 also extends the optical response range. It can be concluded that the activity enhancement of surface-modified TiO2 is mainly attributed to the increase in the photoinduced charge separation rate and to the extent of the optical response range, compared with un-modified ones. Moreover, the inhibition phase transformation mechanism related to Bi2O3 is suggested. (c) 2009 Elsevier B.V. All rights reserved.