Using the first-principles method, the absolute band edge positions were calculated for the (1 1 0) surface of zinc-blende type II-VI semiconductors. The thickness of the slab which was used to model the (1 1 0) surface has significant effect on the band edge positions. The variation trend of E-g with the slab thickness is dominated by that of E-CBM, while almost irrespective of E-VBM. This phenomenon can be interpreted by the electron (at CBM) and hole (at VBM) effective masses. The absolute band edge alignments with different slab thickness can give reasonable interpretation for a series of photocatalytic experiments. (C) 2011 Elsevier B. V. All rights reserved.