Nanoporous ZnO nanostructures were prepared by simple thermal decomposition of plate-like hydrozincite for gas sensor applications. The plate-like hydrozincite obtained through room temperature precipitation had a diameter of 100 nm and a thickness of about 10 nm. After thermal decomposition, nanoporous ZnO nanoparticles on average 30 nm (16.12 nm in crystalline size) in diameter were obtained. Gas-sensing measurements demonstrated that the nanoporous ZnO nanostructures are promising for superior sensitivity ethanol monitoring in lung cancer diagnosis.