In this study, a different method is used to investigate the thermal stability of nitrocellulose, in which the emission of NOx gas from nitrocellulose was monitored and measured by an ion mobility spectrometer (IMS). To do that, the nitrocellulose sample was placed in an especially designed chamber under a temperature of 130 °C, and the released NOx gas was conducted to the IMS. Initially, the positive mode was tried. Although the released NOx was observable, it was not measurable due to the interference of other specious released from the nitrocellulose. Later, the released NOx gas of the nitrocellulose was successfully studied and measured in the negative polarity, using air as the drift gas. The detection limit was obtained to be 2 ppm from the calibration curve. The activation energy and the NOx emission rate were obtained to be 31.4 kJ/mol and 600 nmol/min, respectively.