Hierarchical WO3 nanomesh, assembled from single-crystalline WO3 nanowires, is prepared via a hydrothermal method using thiourea (Tu) as the morphology-controlling agent. Formation of the hierarchical architecture comprising of WO3 nanowires takes place via Ostwald ripening mechanism with the growth orientation. The sensor based on WO3 nanomesh has good electrical conductivity and is therefore suitable as NO2 sensing material. The WO3 nanomesh sensor exhibited high response, short response and recovery time, and excellent selectivity towards ppb-level NO2 at low temperature of 160 ℃. The superior gas performance of the sensor was attributed to the high-purity hexagonal WO3 with high specific surface area, which gives rise to enhanced surface adsorption sites for gas adsorption. The electron depletion theory was used for explaining the NO2-sensing mechanism by the gas adsorption/desorption and charge transfer happened on the surface of WO3 nanomesh.