Xylene (C₈H₁₀) is one of the most hazardous volatile organic compounds, thus highly sensitive gas sensor with real-time monitoring capabilities at lower concentration level is crucial. Hollow and multi-shelled oxide nanostructures are very promising design options for gas sensors due to their low density, high surface area and well-aligned nano-porous structures with less agglomerated configurations. Here, NiCo₂O₄ double-shelled hollow spheres (DHSs) with porous surfaces are successfully synthesized via a self-templating strategy followed by a simple post-annealing process, in which bimetal self-assembly carbonaceous microspheres (CMS) are employed as a sacrificial template. The crystallinity, morphology, and microstructure of NiCo₂O₄ DHSs are detailedly characterized. The formation mechanism of double-shelled hollow structure is also discussed. The as-prepared NiCo₂O₄ DHSs possess large specific surface area as high as ∼93.5 m² g⁻¹, which not only supply outstanding gas permeability and more reactive sites but also accelerate the diffusion of gas molecules. The sensitivity and response time based on NiCo₂O₄ DHSs are 23.3 and 15.4 s to 100 ppm xylene at the optimal working temperature (240 °C), respectively.