Two kinds of different ZnO nanostructures, nanotubes, and nanoflowers were synthesized using an aqueous solution approach. It was demonstrated that the addition of Al3+ and ZnO sol causes the different growth behavior of ZnO nanostructures, and leads to the formation of a nanotube array as well as self-assembled nanoflowers, respectively. The effects of reaction parameters on the morphology of ZnO nanostructures were investigated. The present route reports the possibility for morphology control and assembly of ZnO nanostructures on arbitrary substrates at a low temperature on a large scale.