Abstract: Soybean isoflavone loaded zein composite nanoparticles were prepared by supercritical CO₂ anti-solvent technology. The composite nanoparticles were spherical, as confirmed by atomic force microscope (AFM) . Based on the self-assembly of zein, the average number size of composite particles could be controlled below 200nm with negative surface charge (-22.7 to -34.8mV) , depending on the ratio of zein and soybean isoflavone. Solid state characterization by differential scanning calorimetry (DSC) and fourier transform infrared (FTIR) indicated the hydrogen bond and hydrophobic interaction were thought to be main forces during the formation of soybean isoflavone-zein composite nanoparticles.