Branched hierarchical ZnO nanowire arrays are synthesized on fluorine-doped tin oxide (FTO) substrate via a two-step electrochemical deposition process, which involves the electrodeposition of ZnO nanowire arrays on conductive glass substrate, followed by the electrochemical growth of ZnO nanorod branches on the backbones of the primary ZnO nanowires. The formation mechanism of the branched hierarchical nanostructure is discussed. It is demonstrated that coating the primary nanowire arrays with ZnO nanoparticles seed layer plays a key role in synthesising the branched hierarchical ZnO nanostructure. By adjusting the concentration of Zn(CH3COO)(2) colloid in coating process and the reaction time of the second-step deposition, the density and the length of the secondary nanorod branches in the hierarchical nanostructures can be both varied. Moreover, the photoelectrochemical properties of the dye-sensitized solar cell (DSSC) based on branched hierarchical ZnO nanowire arrays are investigated. Due to the enlargement of the internal surface area within the branched nanostructure photoelectrode, the DSSC consisting of branched hierarchical ZnO nanowire arrays yields a power conversion efficiency of 0.88%, which is almost twice higher than that of the DSSC fabricated using bare ZnO nanowire arrays. (C) 2011 Elsevier Ltd. All rights reserved.