We report here the results of our theoretical investigation on the electronic structure of ZnO/ZnS core/shell quantum dots (QDs) with special emphasis on the atomic charge distribution, electronic energy levels, HOMO-LUMO gap and their variation with thickness of the ZnS shell. We have also studied the possibility of tuning the electronic energy levels of ZnO/ZnS QDs by passivating the surface of the QDs with different ligands. (C) 2012 Elsevier B. V. All rights reserved.