The first in situ fluorescent labeling probe for monitoring of highly volatile methylamine, 8-(4,6-dichloro-1,3,5-triazinoxy)quinoline, has been designed, synthesized and evaluated. The probe labels spectroscopically inert methylamine, causing a large change in fluorescence properties through suppression of the internal charge transfer, and thus can serve as an in situ labeling probe. This applicability has been demonstrated by measuring methylamine released during hydrolysis of N-methylcarbamates such as ethiofencarb.