Abstract: Effective monitoring of toxic and harmful gases and rapid degradation of organic pollutants are essential to reduce the hazards of air and water pollution. In this study, the MoS₂ nanosheets prepared by hydrothermal method were coupled into the ZnO nanoparticles prepared by sol-gel method to form ZnO-MoS₂ nano-composites via a facile ultrasonic chemical route. The structure, morphology and surface chemical component of synthesized materials were characterized by XRD, SEM, TEM and XPS. The characterizations show that multilayer MoS₂ nanosheets are well dispersed among ZnO nanoparticles, and ZnO-MoS₂ composites have good crystallinity and abundant surface defects. The photoelectric properties were explored by UV-vis diffuse reflectance spectrum, photoluminescence spectra (PL) and surface photovoltage spectra (SPV). The results reveal that the formation of ZnO-MoS₂ heterostructure improves the utilization of light and promotes the effective separation of photo-carriers. The UV light-activated gas sensitivity test using NO₂ as the target gas preformed at room temperature saw that the prepared ZnO-MoS₂ gas sensor exhibited excellent gas sensing properties with good sensitivity, recoverability, stability and selectivity, which could effectively respond to low concentration NO₂. The response of the optimized ZnO-MoS₂ sensor with 5wt%MoS₂ to 0.47 mg/m³ NO₂ reached 19.6%. Meanwhile, the gas sensing performance was found to be greatly influenced by the adsorption of O₂ molecule on the surface of the materials, and ZnO-MoS₂ gas sensor possessed much higher gas sensitivity to NO₂ under oxygen free conditions. In addition, the photocatalytic degradation of methylene blue (MB) under simulated sunlight reveal that the ZnO-MoS₂ composites can rapidly remove the high concentration of MB (15 mg/L) in aqueous solution within 40 min by combined action of adsorption and photocatalysis, thereinto, the ZnO-MoS₂ sample with 10wt%MoS₂ shows a reaction rate constant as high as 0.032 min⁻¹. Mechanism analysis shows that the improvement of gas sensing and photocatalytic performance of ZnO-MoS₂ composites mainly attribute to the better absorbability of MoS₂ and the promotion of photocarrier separation rate caused by combination.