This paper reports a chemomechanical explosive sensor based on a thin polymer membrane. The sensor consists of thin parylene membrane and electrodes. Parylene membrane is functionalized with 4-mercaptophenol which interacts strongly with nitrotoluene based explosives. The membrane deflection caused by molecular interaction between the surface and explosives is monitored by capacitance between the membrane and the substrate. To measure the capacitance, electrodes are formed on the membrane and the substrate. While the previous cantilever system requires a bulky optical measuring system, this purely electric monitoring method offers a compact and effective system. Thus, this explosive sensor can be readily miniaturized and used in the field. The developed sensor can reliably detect dinitrotoluene and its limit of detection is evaluated as approximately 110 ppb.