Tungsten disulfide (WS2) nanosheets (NSs) have become a promising room-temperature gas sensor candidate due to their inherent high surface-to-volume ratio, tunable electrical properties, and high on-state current density. For further practical applications of WS2-based gas sensors, it is still necessary to overcome the insensitive response and incomplete recovery at room temperature. In this work, we controllably synthesized high-performance ammonia (NH3) gas sensor based on CuO decorated WS2NSs. The optimized p-p WS2/CuO heterojunctions improve the surface catalytic effect, thereby enhancing the gas-sensing performance. The pure WS2NSs-based gas sensors showed a low response and an incomplete recovery in the case of NH3sensing. After the functionalization of CuO nanoparticles, the WS2/CuO heterostructure-based gas sensor exhibits an improved response value of 40.5% to 5 ppm NH3and full recoverability without any external assistance. Density functional theory calculations illustrate that the adsorption of CuO for NH3is much superior to WS2. The p-p heterojunctions strategy demonstrated in this work has great potential in the design of sensitive materials for gas sensors, and provides useful guidance for enhancing the room-temperature sensitivity and recoverability.