Abstract: The spectral characteristic of the system of I₃^--butyl rhodamine B(BRhB) in 0.08 mol/L HCl were investi-gated by resonance scattering spectroscopy combined with fluorescence, absorption spectroscopy and SEM. It is found that there is an absorption peak at 585 nm, a fluorescence peak at 580 nm and a synchronous fluorescence peak at 570 nm for BRhB. By mixing with I₃^-, the BRhB forms an ion association nano-particle in size of about 60 nm. The nanoparticles exhibit three resonance scattering peaks at 420 nm, 530 nm and 605 nm, and fluorescence quenching at 580 nm, and hypochromic effect at 585 nm. In the range of 2.0×10^-7 to 4.0×^-7 mol/L of iodine, it is found the concentration is proportional to the resonance scattering peak at 605 nm. The spectroscopy and scan electron microscopy results verified the formation of (BRhB-I₃)_n and that the fluorescence quenching, hypochromic and resonance scattering effects are mainly caused by the formation and interface of associated nanoparticles.