A novel fluorescence enhancing probe for Hg2+,3′,6′-bis(diethylamino)-2-((2-hydroxy-4-methoxybenzylidene)amino)spiro［isoindoline-1,9′-xanthene］-3-thione (RBS),was designed and synthesized.Its structure was characterized with IR,elemental analysis and 1H NMR spectra.The fluorescence intensity of probe solution is very weak,but after combination with Hg2+,its fluorescence intensity increased obviously.Thus,a new method for the determination of Hg2+ was established.It exhibits a dynamic response concentration range for Hg2+ from 5.00×10-9 mol/L to 1.10×10-6 mol/L with a detection limit of 2.82×10-9 mol/L.The method showed advantages of simplicity,high sensitivity,excellent selectivity and wide linear range,and was applied in the determination of Hg2+ in real sample with satisfactory result.