Self-assembled casein nanoparticleswere prepares via acid induction and thermal induction,and aquercetin delivery system was constructed.Then,the interaction mechanism and the effect of quercetin on casein conformation were investigated by means of fluorescence spectroscopy and dynamic light scattering.The results indicate that ( 1) quercetin can quench the intrinsic fluorescence of casein; ( 2) casein nanoparticles at pH5. 5 after heat treatment possesses the strongest binding with quercetin; ( 3) the interaction between quercetin and casein is a spontaneous and exothermal process,and the main force in this process is hydrogen bonding; ( 4) the interaction between quercetin and casein nanoparticles has no great effect on the self-assembly characteristics of casein; ( 5) quercetin after a 30-day storage keeps stable; and ( 6) casein nanoparticles after a heat treatment at pH5. 5 is of the highest retention rate up to 75. 38%.