Abstract: There is a maximum absorption peak at 530 nm and a fluorescence peak at 550 nm for rodamine 6G(RDG) in the medium of 0.02 mol/L HCl. The PtI₆^2- and RDG⁺ combine into hydrophobic PtI₆-2RDG association molecule by means of attraction force. There is strong Van de Waals force and hydrophobic force among PtI₆-2RDG molecules. So it form (PtI₆-2RDG)_n composite nanoparticle in size of about 40 nm and red-violet color. Which exhibits a resonance scattering peaks at 470 nm, two characteristic resonance scattering peaks at 590 nm and 400 nm, and enhanced resonance scattering effect. The fluorescence quenching at 550 nm and absorption decreasing at 530 nm are owing to that the RDG molecules in the body of the nanoparticle can not absorb the incidence photons and may be not excited by it. So that, the RDG molecules do not emit fluorescence, absorption photon RDG molecules in the system decrease greatly. The (PtI₆-2RDG)_n nanoparticle can be decomposed into PtI₆-2RDG association molecule by alcohol. Meanwhile, the resonance scattering peaks and the red-violet disappear. And the A_{520 nm} and F_{550 nm/510 nm} come back. The results demonstrate that the formation of (PtI₆-2RDG)_n association nanoparticle in red-violet color and the interface between the nanoparticle solid phase and the water phase is the results in its enhanced resonance scattering, two characteristic resonance scattering peaks at 590 and 400 nm, fluorescence quenching and hypochromic effects.