We report for the first time, development of an efficient ethanol sensor using mild functionalized multiwalled carbon nanotubes (MWCNTs). A unique technique to functionalize MWCNT is reported to enhance the performance of the ethanol sensor based on it. The conventional functionalization techniques tend to damage physical structure of carbon nanotubes (CNTs) to a large extent and convert most of their sp2 bonds into sp3 bonded carbon atoms. This results in reduction of the available adsorption sites for ethanol vapors on the CNT surface and hence deteriorates the sensitivity. In this work, the functionalization of nanotubes is achieved through direct cycloaddition to π electrons of the CNT that does not hamper the physical structure of the nanotube. High resolution transmission electron microscopy (HRTEM) and Raman spectroscopy studies were employed to confirm the appropriate functionalization for better performance of the sensor. Electrical transport properties of the composites were also studied to understand the quality of the established CNT network. Out of the other functionalization technique, Diels Alder cyclo addition reaction based composite sensor was found to exhibit excellent performance and has an edge over the other reported CNT based sensor. © 2014 Elsevier Ltd. All rights reserved.