High stable triethylamine gas sensors under different relative humidity are highly desirable in order to correctly detect the concentrations of target gas. In this study, a series of Sn-doped NiO hollow nanofibers were prepared through a facile electrospinning process followed by heat treatment. Sn doping could inhibit the crystal growth, and the crystal sizes would decrease with the increase of Sn doping concentration. Gas sensing investigation indicates that Sn doping could significantly enhance the gas response towards triethylamine at a relative low temperature. Especially, the gas sensor exhibits the highest response to triethylamine when the doping content of Sn reaches to 6 at%. The response value is about 16.6–100 ppm triethylamine, and it is ∼9.2 times higher than that of pure NiO nanofibers at the same operating temperature. In addition, the resistances of the gas sensors with different doping contents of Sn would change differently in air or in target gas under variable relative humidity. The resistances in target gas are almost unchanged with the increase of relative humidity with the Sn doping content of 6 at%. It is reasonable to speculate that Sn doping can heavily alter the surface state of NiO nanofibers, which is beneficial for the improvement of the gas response and humidity dependence properties.