In this work, we developed a novel colorimetric and ratiometric fluorescence probe for the selective and sensitive monitoring of cysteine based on a coumarin Schiff-base platform. This probe exhibited remarkable AIE characteristics with an exceptionally large blue shift (125 nm), which showed low emission in DMSO but strong aggregation-induced emission in water solution. An excellent linear relationship of fluorescence intensity ratio (F₄₅₀/F₅₇₅) (R² = 0.9922) versus Cys concentration in the range of 1–13 μM was obtained.