We used an electrospinning method to produce ZnO nanofibers for CO sensing. ZnO nanofibers were electrospun from a solution containing poly(4-vinyl phenol) (PVP) and Zn acetate. The calcination process of the ZnO/PVP composite nanofibers brought forth polycrystalline wurtzite ZnO nanofibers with diameters of 30-70 nm. Regarding the applications of the ZnO nanofibers, their CO gas-sensing responses were evaluated in a concentration range of 10-25 ppm. The resistances of the ZnO nanofibers were observed to decrease upon exposure to CO. This is attributed to the reducing nature of CO, which reacts with adsorbate O(-) to release an extra electron.