A synchrotron radiation source was utilized for X-ray photoelectron spectroscopic analysis of a nitrobenzaldimine-formed monolayer. The N(1s) peak intensity for the nitro group becomes reduced upon X-ray irradiation, while C(1s) and O(1s) peaks are invariant. This observation indicates that the nitro group is cleaved selectively, leaving the phenyl ring intact in the layer. The cleavage rate is measured as a function of photon energy and normalized with the photon flux. The cleavage is first-order to the concentration of the nitro group. The rate constant is independent of the incident photon energy, suggesting that the cleavage is not associated with a direct photoexcitation of atomic core electrons. Electrons ejected by the X-ray are proposed as the most viable cause for the bond cleavage. The molecules remaining on the irradiated surface were analyzed with gas chromatography-mass spectrometry coupled with the solid-phase microextraction method after hydrolyzing the imine bond. It is found that the amount of nitrobenzaldehyde is reduced upon the irradiation, but the expected products, benzaldehyde and hydroxybenzaldehyde, are not produced.