In the last decades, nanocomposites made of polymer matrix filled with carbon nanotube (CNT) have been a great topic of studies, particularly as concerns the rheological behavior and the electrical property under shear. In contrast, this work focuses on the deformation of the CNT network in elongated polymer melts by a combination of conductivity monitoring and extensional rheological measurement. For this specific purpose, an extensional viscosity fixture accessory of a rotational rheometer ARES has been modified to allow the sample conductivity measurement. This new setup gives access to the measurement of the electrical conductivity simultaneously with the extensional stress under extensional deformation. First results have shown that the conductivity of CNT/polystyrene nanocomposites can present a sharp decrease before the sample break and this decrease appears more rapidly for higher extensional rates and lower temperatures. The results have been correlated to experimental conditions via the introduction of the Weissenberg number. (c) 2017 The Society of Rheology.