It is important to detect decomposition of insulating gas SF6 caused by partial discharges for gas-insulated switchgear (GIS). In the previous result, the author developed a novel partial discharges sensing using carbon nanotube (CNT) gas sensor. In recently, an application of high voltage DC for long distance electric power transmission has been often used in various countries as the interconnection system and overload demand. In this study we applied the CNT gas sensor to detect partial discharges generated by high voltage DC. There was polarity profile for DC compared AC discharges. It was found, response of the sensor in the case of negative discharges was much higher than positive discharges under the same experimental condition. And the decomposed gases for each case were identified by FT-IR spectroscopy. The result indicated absorption peaks correspond to SF4 and SOF2 of positive discharges was much higher than that of negative discharges.