Band alignments of ZnO/CdSe nanocrystal quantum-dots (NQDs) heterojunctions are determined by ultraviolet photoelectron spectroscopy using synchrotron radiation source. To obtain ideal heterojunction interface, 1,2-ethanedithiol was used for CdSe NQDs as a ligand substitute. A type II band alignment of the ZnO/CdSe NQDs heterojunctions with changeable band offsets by varying the sizes of CdSe NQDs is concluded. The tunable band alignment of ZnO/CdSe NQDs heterojunctions is beneficial to the improvement of the design and fabrication of quantum-dot-sensitized solar cells. (C) 2013 Elsevier B.V. All rights reserved.