Flat-Band (FB) potentials of TiO2 and SnO2 nanoparticles shifted negatively once they were coated with a thin insulating MgO layer. For core-shell structured TiO2-MgO and SnO2-MgO composites, incorporation of 1% (w/w) of MgO results in negative shift in FB potential of TiO2 and SnO2 nanoparticles by -0.15 eV and -0.38 eV, respectively. The negative shift of FB increased with the increase of MgO content. The highest shifts in FB potential reached -0.85 eV and -0.65-0.70 eV (vs Standard Calomel Electrode) when MgO content was equal to 10% (w/w) and 10-15% (w/w) for SnO2 and TiO2 respectively. In this investigation, interconnection between the negative shift in FB potential and the efficiencies of dye sensitized solar cells based on the prepared materials are discussed. (C) 2008 Elsevier B.V. All rights reserved.