Highly porous ZnO nanoflakes were successfully prepared using a microwave-assisted hydrothermal method. The presence of aluminum changes the environment of the preparation reaction, which controlled the crystallographic orientation. The unique morphology and properties of ZnO nanoflakes may be due to the effect of microwave irradiation and the ambient condition. The approach is very simple and there is rapid growth of around 3 μm ZnO within 30 min. The mechanism of the construction of unique ZnO nanoflake growth using the present approach is proposed. Hence, the prospective performance of ethanol vapor sensing for the rapid growth of ZnO porous nanostructures was investigated.