In order to improve the sensing-properties of carbon nanotube based composite for potential applications in chemical sensors, CNTs/PANi core/shell-structured nanowires were prepared with in-situ polymerization approach. A series of characterizations was carried out by TEM (transmission electron microscopy), the Fourier-Transform Infrared (FTIR) spectra, and so on. A chemical prototype sensor was constructed based on CNTs/PANi core/shell-structured nanowires and interdigital-structured electrodes on flexible polymer substrate. The gas-sensing behaviors of the sensor to some gases operating at room temperature were examined. Results showed that the sensitivity of CNTs/PANi core/shell-structured nanowires was increased dramaticly compared with pure carbon nanotube materials. This provides a carbon nanotube based composite materials with enhanced gas-sensitivity, which would have potential applications in some chemical sensors.