This paper presents the construction and analytic properties of a piezoelectric sensor with a cyclohexanone-formaldehyde polymer coating. The sensor was constructed on the basis of a quartz resonator with a resonance frequency of 9 MHz by coating its surface with polymer layers changing the resonance frequency by 10 kHz. The sensor is highly sensitive to aromatic nitro-compounds. Its sensitivity to nitrobenzene vapour is 0.73 Hz/μg 1 −1 (4 Hz/ppm). An attempt was made to assess the type of intermolecular interactions which determine the sensitivity of the sensor. The sensor was used to determine nitrobenzene in air and results were compared to those obtained from measurements performed by gas chromatography.