Gas-sensing properties of metal-oxide nanocomposites are largely depended on their structures and compositions. It remains great challenges to design well-defined heterostructures to improve gas-sensing properties and establish the relationship between these properties with heterostructures. In this paper, an extremely sensitive ethanol sensing material via decoration of NiCo2O4 nanosheets onto 1D alpha-MoO3 nanorods by a facile chemical deposition method was developed. The structures and compositions of the as-prepared sensing materials were characterized by XRD (X-ray diffraction), SEM (scanning electron microscopy) and TEM (transmission electron microscopy). It was revealed that uniform porous NiCo2O4 nanosheets grown on the surface of alpha-MoO3 nanorods backbones with a low lattice mismatch at the interface of heterostructures, Gas-sensing tests showed that this novel NiCo2O4/alpha-MoO3 nanocomposite exhibited superior sensing performances for ethanol with high response, negligible cross-responses to other interfering gases and excellent stability. The response to 1 ppm ethanol was about 20 (R-g/R-a), whereas pure NiCo2O4 and alpha-MoO3 showed almost no response. Notably, the detection limit for ethanol was as low as 50 ppb (R-g/R-a = 2.7). The enhanced sensing properties were attributed to the unique structures and heterojunctions between NiCo2O4 nanosheets and alpha-MoO3 nanorods. The results above indicated the potential of this as-designed NiCo2O4/alpha-MoO3 nanocomposite to detect sub-ppm level ethanol in a highly sensitive manner. (C) 2019 Elsevier B.V. All rights reserved.