With CH3COONa/(CH3COO)(2)Cu as the electrolyte system, nanometer Cu2O thin film is fabricated by means of electrodeposition at TiO2/ITO electrode under the weak acid environment. The crystal morphology of nanometer Cu2O thin film is characterized by XRD, SEM and XPS. The effects of KCl-doping and annealing treatment upon nanometer Cu2O crystal morphology, thin film response to visible light and open circuit voltage are studied. The mechanism of KCl-doping to control thin film morphology is discussed. The results indicate that with the increase of KCl concentration, making nanometer Cu2O thin film compact, the average grain diameter and the open circuit voltage increase, and the forbidden band width decreases, and exhibited obvious absorbance response in visible light range, the preferred orientation character of Cu2O crystal has changed from the obvious (111) face preferred orientation into the obvious (200) face preferred orientation. The crystal morphology of nanometer Cu2O thin film has changed from regular octahedron into truncated cube when the KCl concentration reaches 7.0 mmol L-1. The transformation of nanometer Cu2O thin film morphology is caused by the preferential adsorption of Cl- at the (200) crystal face of Cu2O crystal. (C) 2014 Elsevier B.V. All rights reserved.