Monitoring of argon gas dissociation was demonstrated using a matted sheet of single-walled carbon nanotubes (SWNTs), prepared by alternating current dielectrophoresis. The conductance of the SWNT network increased upon exposure to dissociated byproducts induced by corona discharge (CD), and the sensor signal was recovered rapidly by purging with the pure argon. Similar experiments on argon plasma were also carried out to investigate the applicability of the SWNT sensor in the monitoring of plasma-induced dissociation. The transduction mechanisms in both CD activity and plasma were analyzed using Raman spectroscopy. The results show that the detection of argon dissociation generated inside the reaction zone is possible using a miniaturized SWNT sensor.