Much attention was paid on ultrasound for its application in food process and preservation.Ultrasound has been studied in milk pasteurization; however,the influence of ultrasound on the properties of casein in milk was few reported.Casein accounts for 80% of total protein in milk and plays a great role in the properties in milk.In addition,Peptides derived from casein which is difficult to be digested exhibit a variety of bioactivities.Effect of ultrasound on the stability and digestion of casein in milk was investigated in this paper.Effects of time and power of ultrasound pretreatment on the hydrolysis degree of casein were investigated.As for stability,it was shown that after ultrasound average diameter of casein micelles decreases,which is associated with the cavitations of ultrasound,so ultrasound treatment could improve the stability of casein and it is a novel method with potential application during milk process.