Monoamine inclose (MAO) A is a flavoenzyme that catalyzes the oxidation of biologically important monoamines and is thought to be associated with psychiatric disorders. Here, we report a strategy for rationally designing a F-19 magnetic resonance imaging probe for the specific detection of human MAO-A (hMAO-A) activity. Our designed F-19 probe was oxidized expeditiously by hMAO-A to produce 2-fluoro-4-nitrophenol via a spontaneous beta-elimination mechanism. Concomitant with the structural change of the probe to the product, the F-19 chemical shift changed by 4.2 ppm, which was enough to visualize the probe and enzymatic product separately. Importantly, our probe achieved excellent discrimination of hMAO-A from its isoform hMAO-B.