Different sizes of ZnWO4 photocatalysts were synthesized by a hydrothermal method. The as-prepared sample shows highly efficient photocatalytic activity for the degradation of RhB under UV irradiation, which significantly vary with the increase of the hydrothermal temperatures. Surface photovoltage spectrum (SPS), field-induced surface photovoltage spectrum (FI-SPS) and surface photovoltage transient (TPV) techniques are used to investigate the detailed photoinduced charge transfer behavior. Results indicate that the ZnWO4 synthesized at 413 K possess the largest BET surface area and the abundant donor surface states which are assumed to inhibit the recombination of the photogenerated electron-hole pairs, and thus a significant enhancement in the reaction rate is observed. (C) 2010 Published by Elsevier B.V.