SnO₂/NiO composite semiconductor nanofibers with different Sn contents were prepared by electrospinning combined with chemical precipitation and high temperature calcination. Morphology, structure and elemental content of the samples were characterized. Taking ethanol as the target gas, the gas sensing properties of SnO₂/NiO nanofibers and the influence of Sn content on the gas sensing properties of the composite nanofibers were investigated. The results show that the SnO₂/NiO composite nanofibers have a three-dimensional network structure, and the SnO₂ composite can significantly enhance gas sensing properties of NiO nanofibers. With the increase of SnO₂ content in composite fibers, the response of samples to ethanol is enhanced. Among them, the SnO₂/NiO nanofibers with the highest sensitivity show response value of 13.4 to 100×10^-6 ethanol (volume fraction) at the optimum working temperature of 160 ℃. The maximum response value of the SnO₂/NiO nanofibers exhibits 8.38 times enhancement compared to that of NiO nanofibers. Compared with comercial MQ-3, a commonly used ethanol sensor, the SnO₂/NiO composite nanofibers have lower optimal working temperature and higher response sensitivity, which shows great potential in practical application.