A novel ratiometric fluorescent probe BCB was reported for the first time for the sensitive and selective analysis of Ag+ based on two Boradiazaindacene (BODIPY) as both the reference fluorophore and recognition part. Upon the addition of Ag+ ions, a strong fluorescence emission at 570 nm from recognition BODIPY would be appeared, whereas the fluorescence of the other BODIPY at 535 nm would be a constant reference fluorescence signal. As a result, the ratio of fluorescence intensity (λ570/λ535) was changed from 0.16 to 1.0. And the selectivity of BCB towards Ag+ over other metal ion was excellent. Other metal ions, such as Cd2+, Cu2+, Fe3+, Hg2+, Mg2+, Ni2+, Pb2+ and Zn2+ showed negligible changes in the both absorption and fluorescence spectra of BCB.