Hollow NiO–SnO₂ nanospheres have been fabricated via a simple one-pot template-free method. The synthesis is based on solvothermal treatment of stannate and nickel nitrate as the precursor in a mixed solvent of heptane–ethanol. The hollow nanospheres show diameters of about 200–300 nm with the wall thickness of about 50 nm, and the shell consists of numerous small nanoparticles. The gas sensor based on hollow NiO–SnO₂ nanospheres exhibits high response and quick response–recovery to NH₃, which are much better compared with sensors based on solid NiO–SnO₂ nanospheres. The enhanced sensor performances are attributed to the larger surface area and fast gas diffusion.