NiO nanofibers were synthesized by an electrospinning method with polyvinyl alcohol and nickel acetate tetrahydrate as precursor materials. Individual nanofibers consisted of nanograins. A gas sensor has been fabricated using these nanofibers. Its sensing properties to NO2 and benzene were investigated. The sensor exhibited good sensitivity and dynamic properties for the tested gases. All these results suggest that the electrospinning-synthesized NiO nanofibers hold promise for realizing sensitive and reliable gas sensors.