Abstract: Under the conditions of 0.01 mol/L HCl-8.0 10^-4 mol/L KI, there is a fluorescence peak at 550 nm for Rhodamine 6G (RhG). When there is IO₃^-, it reacts with I^- to form I₃^-. RhG and I₃^- combine an ion association particle. The particles exhibit three resonance scattering peaks at 320, 400 and 610 nm and a synchronous scattering peak at 470 nm. And there is fluorescence quenching at 550 nm. IO₃^- concentration in the range of 2.0 to 100×10^-7 mol/L is proportional to the fluorescence quenching intensity at 550 nm. A new fluorescence quenching method has been described for the determination of IO₃^- in salt samples. The spectral results have been verified that the formation of (RhG-I₃)_n association particles and the interface is main factor that cause the fluorescence quenching effects.