Abstract: In this paper, the effects of p H, the concentration ratio of sodium caseinate ( SC) to gum arabic ( GA) , the total concentration of SC and GA and the ionic strength ( the concentration of Na Cl) on the interaction between SC and GA and the formation of nanoparticles were investigated by the characterization of turbidity, particle size and zeta potential. The morphological attributes of the nanoparticles were characterized by transmission electron microscopy ( TEM) and the storage stability of nanoparticles was studied. Furthermore, the mechanism of the formation of nanoparticles formed by interaction between SC and GA was researched by infrared spectroscopy ( FTIR) and fluorescence spectroscopy.The results revealed that p H and ionic strength greatly influenced the interaction between SC and GA and the formation of nanoparticles, indicating that the main force to form nanoparticles between SC and GA was electrostatic interaction. Meanwhile, the formation of stable nanoparticles was achieved under the following conditions: the concentration ratio of SC to GA was 1 ∶ 1, p H was 4.2, the total concentration of SC and GA was 3.0 mg/m L and the concentration of Na Cl was 10 mmol/L. The particle size of resulted nanoparticles was about 142 nm and zeta potential was about-21.43 m V. Moreover, the nanoparticles remained stable after storage of one month at 4 ℃. TEM results showed that the nanoparticles were spherical in shape. FTIR results confirmed that electrostatic interaction occured in positively charged amino of SC and negatively charged carboxyl of GA. The fluorescence spectra results demonstrated that the combination between SC and GA to form nanoparticles by electrostatic interaction was low affinity.