The fluorescence quenching of the Tb-BPMPHD-CTMAB by nucleic acids is reported. The maximum fluorescence quenching was obtained at pH5.5, with maximum excitation and emission wavelengths at 300 and 543nm, respectively. Under optimal conditions, the differential value of fluorescence intensity between the absence and presence of nucleic acids was proportional to the concentration of nucleic acids over the range of 4.0x10−8∼ 1.0x10−5g/ml for fsDNA and 2.5x10−8∼ 6.15x10−6g/ml for yRNA, respectively. The corresponding detection limits are 9.0ng/ml for fsDNA and 5.0ng/ml for yRNA. The method was applied to the determination of DNA (or RNA) in synthetic samples. The results obtained were satisfactory.