Hierarchical nanostructured Al-doped ZnO (AZO) powders were successfully prepared through a mild solution route. The crystal structure and morphology of AZO were determined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The morphology of the samples changed from random flower-like nanostructures to uniform flower-like hierarchical nanostructures with different Al doping contents. The optical and electrical properties of AZO were studied by UV/Vis spectroscopy and four-point probe. The optical band gap of AZO increased initially but then decreased as the Al content was increased owing to the Burstein–Mass effect and the many-body effect. Conversely, the electrical resistivity of the AZO powders first decreased and then increased with the Al doping content increasing because of changes in the electron and dopant concentrations. AZO exhibited the smallest electrical resistivity with an Al doping content of 1.0 at-%, which is two orders of magnitude smaller than the electrical resistivity of ZnO.