A novel vapor sensor is fabricated with polycaprolactone-grafted-carbon black (CB-g-PCL) as sensing materials. The influence of PCL with different grafting contents and solvents with various solubility and concentrations including benzene, deionized water, epoxy chloropropane (ECP), ethanol, toluene, and tetrahydrofuran on the response of electric resistance was investigated. When compared with mixture of PCL and carbon black, the CB-g-PCL-based sensor shows high sensitivity and good reproducibility. Sensor with moderate content of grafting PCL showed high sensitivity to vapors. The electric resistance of sensor drastically increased in ECP, ethanol, and deionized water with similar solubility with PCL and showed slight increase in benzene, toluene, and tetrahydrofuran with different solubility. The study on the response of electric resistance of CB-g-PCL to different vapors confirmed the swelling-induced sensing mechanism of sensor based on polymer-grafted-conductive nanomaterials. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 3277-3282, 2011