Abstract: The shear stress caused by flowing liquid and the tensive stress caused by the rapid decrease in pressure in high-pressure homogenizers have been studied through soymilk homogenizing experiments, and their orders of magnitude have been estimated. It is shown that in those grains of low Young's modulus, the tensive stress resulted from rapid decrease in pressure may be as significant as the shear stress is, and they both play important roles in the homogenizing process.