A ratiometric fluorescence probe based on carbon quantum dots with 420 nm emission (bCQDs) and a p-phenylenediamine-derived fluorescence probe with 550 nm emission (yprobe) is constructed for the detection of Mn 2+ . The presence of Mn 2+ results in the enhanced absorption band at 400 nm of yprobe, and the fluorescence of yprobe is significantly enhanced based on the chelation-enhanced fluorescence mechanism. The fluorescence of bCQDs is then quenched based on the inner filtration effect. The ratio (I 550 /I 420 ) linearly increases with the increase of Mn 2+ concentration within 2.00 × 10 -7 -1.50 × 10 -6 M, and the limit of detection is 1.76 × 10 -9 M. Given the fluorescence color changing from blue to yellow, the visual sensing of Mn 2+ is feasible based on bCQDs/yprobe coupled with RGB value analysis. The practicability of the proposed method has been verified in tap water, lake water, and sparkling water beverage, indicating that bCQDs/yprobe has promising application in Mn 2+ monitoring.