Certain amount of Cr2O3 has been in si tu added to ZnO nanofibers during the electrospinning process and subsequent calcination to form Cr2O3-sensitized ZnO (C-s-Z) nanofibers. The morphology and structure of the as-prepared nanofibers have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and X-ray diffraction (XRD). The effect of the Cr2O3 component in C-s-Z nanofibers on the gas sensing properties has been evaluated by the responses to ethanol vapor. The results have showed that the C-s-Z nanofibers containing 4.5 wt% Cr2O3 exhibit the best sensing properties to ethanol vapor. The response to 1 ppm ethanol vapor is as high as 3.6, and the response and recovery time ate about 1 and 5 s, respectively. In addition, the as-prepared sensors exhibit excellent selectivity and stability. These results indicate that the C-s-Z electrospun composite nanofibers can be used in fabricating high performance gas sensors. (C) 2009 Elsevier B.V. All rights reserved.