ZnO nanofibers were synthesized using an electrospinning method with polyvinyl alcohol and zinc acetate as precursor materials. The ZnO nanofibers of a polycrystalline nature were distributed uniformly over the substrate. Individual nanofibers consisted of nanograins. Using these nanofibers, we have fabricated a gas sensor. The sensing properties of the ZnO nanofiber sensor to NO(2) and CO were systematically investigated. It exhibited device-applicable sensitivity and dynamic properties for the tested gases, demonstrating that the electrospinning-synthesized ZnO nanofibers hold promise for realizing sensitive and reliable gas sensors.