Co–ZnO composite nanofibers (0, 0.2, 0.4, and 0.8 wt%) are synthesized by electrospinning and calcination techniques. The fiber diameters are found to decrease by increasing the Co content in the ZnO nanofibers. The m-xylene sensing properties of the ZnO nanofibers are effectively enhanced with appropriate Co amount. The best sensing properties are found based on the 0.4 wt% Co–ZnO composite nanofibers at 320°C. The corresponding response is up to 14.8 when the sensor is exposed to 100 ppm m-xylene, and the response and recovery times are about 4 and 6 s, respectively. Moreover, excellent selectivity is also observed in the sensing investigation. The results make Co–ZnO composite nanofibers good candidates for fabricating high performance m-xylene sensors.