Nano-sized cellulose has excellent characters.The paper used soybean dregs which are rich in cellulose as raw materials.The grinding soybean dregs were pretreated by hydrochloric acid.The pretreatment conditions are 3 mol/L HCl in concentration,hydrolyzation temperature 100 ℃,hydrolyzation time 120 min,acid water to material ratio 50∶ 1.The soybean-dreg cellulose pretreated with HCl and dried was hydrolyzed with cellulase.The optimum preparation technology of nano-sized soybean-dreg cellulose was investigated by single factor and orthogonal experiments: cellulase dosage 3 000U/g,pH 5.0,hydrolyzation temperature 55 ℃,hydrolyzation time 6 h,water to material ratio 20 mL/g.The size of nanocrystalline cellulose with globosity appearance was 15~50 nm through scanning electron microscope and transmission electron microscope.