A new rugby-like ZnO thin film was self-assembled via a hydrothermal method and the influences of the hydrothermal temperature on crystal growth and gas sensing properties of ZnO thin films were investigated. The results showed that the highly porous rugby-like ZnO crystals were self-assembled via thin fan-shape sheets with abundant nanopores formed by interconnected the smaller nanoplates when the hydrothermal temperature was 140 degrees C. Its specific surface area value reached 45.0 m(2) g(-1). The sensor exhibited an excellent gas sensing response, a good selectivity towards formaldehyde and quick response characteristics at the optimum working temperature of 250 degrees C.