Swelling is generally assumed to be the key operating mechanism in polymer nanocomposite chemical sensors.Here the swelling kinetics has been correlated to the sensor electrical performances. In this study, poly(2-hydroxyethyl methacrylate)/ carbon black nanocomposites have been deposited on silicon or alumina substrate and have been used as sensing layer for conductive chemical sensors. A kinetics study of the device swelling characteristic and of the electrical response to ethanol vapors was performed. Filler structure and morphology have been found to differently affect the polymer nanocomposite swelling behavior. Results are used to optimize sensing layer fabrication and thus improve sensor performances.