The Ag metal core-TiO2 shell (Ag@TiO2) composite nanocluster with uniform size, shape and core-shell structures was successfully synthesized by a new simple citrate reduction method. The core-shell structure of Ag@TiO2 nanocluster was characterized by using TEM, SEM, XPS, EDX, XRD, and photoluminescence spectra analysis. It was found that the Ag core is in metallic form which is covered by TiO2 shell within 3-5 nm thickness and the core-shell particles size was about 30 nm. The photocatalytic and photothermal cell killing efficiency of colloidal Ag@TiO2 core-shell nanocluster was evaluated against cancer (HeLa) cells under UV-vis irradiation. It was found that the Ag@TiO2 nanocluster with an adequate Ag ratio to TiO2 killed more malignant (HeLa) cells by 80% compared to TiO2 nanoparticles alone. The comparative study of the cell viability using UV only, visible only and UV-visible light revealed that the synergy effect of photocatalytic hydroxyl radical formation and Ag-plasmonic photothermal generation plays a vital role for the cancer cell killing. Based on the obtained results, a plausible mechanism was also proposed. (C) 2011 Elsevier B.V. All rights reserved.