Abstract: Anew sensitive fluorescence quenching method is proposed on the basis of the ternary complex formed from ruthenium (Ⅲ) and rhodamine 6Gin the presence of thiocyanate. Rhodamine 6G is a fluorescent dye. Its maximum excitation wavelength is 525nm, and its maximum emission wavelength is 551nm. The formation of the ternary complex reduces the fluorescence. Beer's law is obeyed in the concentration range from 0 to 0.7/μg/50ml. The method is valuable in determining the trace of ruthenium in both synthetic and natural samples.