Acridone-labeled BDF bases (Ac)A and U-Ac were incorporated into oligonucleotides (ODNs) and their photophysical properties were evaluated. The BDF probe containing (Ac)A is extremely powerful in recognizing opposite base T via enhancement of the fluorescence intensity. Furthermore, they emit strong fluorescence at a longer wavelength than previously reported pyrene-labeled BDF probes and thus can be used for the detection of SNPs.