In this paper, we report the synthesis, characterization and investigation of the optical properties of a new fluorescent probe, 4ʹ-nitroolefinylflavone (4ʹ-NOF) 1, based on a flavone skeleton and bearing a nitroolefin moiety. Upon the addition of cysteine, a remarkable fluorescence enhancement (200 fold) was observed for probe 1 accompanied with a slight blue shift from 457 nm to 459 nm. The prepared probe displays high selectivity and sensitivity towards cysteine over other amino acids. The Michael addition of cysteine to probe 1 was confirmed by 1H-NMR spectroscopy. The detection limit of probe 1 towards cysteine was found to be 1.63 μΜ, a lower concentration than the normal human cysteine level, 30-200 μΜ.