The preparation characteristics of monodispersed oil-in-water (O/W) emulsions with large particles stabilized were investigated by using isolated soybean protein as emulsifiers. Monodispersed emulsion was successfully prepared when pH value ranged from 6 to 8. The particle became significantly bigger and its monodispersity decreased with the decrease of pH value. Emulsions were prepared using isolated soybean protein with a particle size of 43.4μm, and whose coefficient of variation was 4.3% when pH value of protein solution was 7. When the pH value of protein solution was lower than its isoelectric point, the electronic attractive interaction worked between the negatively charged silicon MC plate and the positively charged protein molecules, resulting in unsuccessful emulsification.