In acid medium, rhodamine B(RhB), rhodumine S(RhS),rhodamine 6G(RhG) and butyl rhodamine B(b-RhB) have a fluorescence peak at 580, 549, 553 and 580 nm,respectively. BrO3- oxidizes excess I- into I3-. Rhodamine dyes combine I3- to form ion association nanoparticles,resulting in fluorescence quenching at 580, 549, 553 and 580 nm, respectively. The fluorescence quenching intensity is proportional to the concentration of BrO3- in the range of 0.020 4 - 0.710 μg/mL for RhB, 0.025 - 0. 512 μg/mL for RhS, 0.025- 0.260 μg/mL for RhG, 0.025- 1.28 μg/mLfor b-RhB, respectively. In the four systems, RhB system has good stability and high sensitivity. Thus, a simple,sensitive fluorescence method was proposed for the determination of BrO3- in commercial bread additives and flours, with satisfactory results. The results of the fluorescence spectra and scan electron microscopy show that the formation of about 60 nm (RhB - I 3)n association nanoparticles and the interface between the nanoparticles and solution are main factors that cause the fluorescence quenching.