Films of poly[3-(butylthio)thiophene] were prepared via Langmuir-Blodgett (LB) deposition for applications in gas sensor devices. A description of the LB deposition or the sensing layer starting from a mixture of polymer and arachidic acid is given. Alumina substrates equipped with gold interdigitated electrodes have been used. In particular, the samples so prepared show variation in the electrical conductivity when exposed to NO2 oxidising agent at a working temperature of about 80 degreesC. Selectivity towards NO2 with respect to other different gases like ammonia, carbon monoxide, ethanol, methanol and methane has been evaluated.