[en] Highlights: • NiO nanoflowers with various morphologies exhibit excellent gas response. • A growth mechanism for NiO nanoflower has been established. • Surfactant plays a critical role in the formation of NiO nanostructure. The NiO nanoflowers were prepared by a facile surfactant assisted hydrothermal method using Ni(NO₃)₂–6H₂O or NiCl₂–6H₂O as precursor compound. The microstructure of the samples was characterized by SEM and XRD. The gas sensing properties of the NiO nanoflowers toward ethanol was also investigated. The results show that surfactant plays a key role in the synthesis of flower-like NiO. The NiO nanoflowers show excellent sensing performances to ethanol gas. This morphology holds substantial promise for applying NiO as a potential gas sensing material for future sensor application.