High-purity ZnO nanowires, which possess branching structures, were prepared by evaporating metal zinc onto thermally oxidized Si wafer. The morphology and microstructure analyses of ZnO crystals were performed by scanning electron microscopy and high-resolution transmission electron microscopy. The nanowires possess hexagonal wurzite structure. The I-D growth mechanism of ZnO nanowires corresponds to Sears theory. Multiply twinned ZnO fine particles deposited on silica surfaces serve as the growth centers of branching structure. The dendrite ZnO nanowires have potential for building optoelectronic nanodevices with special configurations or as building blocks in the construction of functionalized interfaces.