Irradiation of rufloxacin (RF) under aerobic conditions gives rise to N-demethylation of the piperazinyl ring, which is enhanced in aerated D₂O. Two primary processes seem to be involved in RF N-demethylation: photoionization from ¹RF and singlet oxygen generation from ³RF. Both processes may lead to the same key intermediates, namely, RF^· and superoxide radical anion; coupling of these intermediates explains N-demethylation of RF via an iminium cation. Formation of the hydrated electron by a monophotonic process (with a quantum yield of 0.09) is detected along with ³RF (with a intersystem-crossing quantum yield ϕ_ISC = 0.36) by laser flash photolysis. Studies performed on RF methyl ester give qualitatively similar results.