In a batch wise constant-rate expression process, a material is compressed at a constant deliquoring rate by increasing the expression pressure. When the pressure reaches a specified, predetermined value, the pressure is held constant until the final equilibrium compression is obtained. In this paper, the constant-rate expression process of homogeneous semisolid materials is discussed and a method for analyzing this constant-rate process is presented. The following assumption is made: the internal condition of consoh''dated cake is the same under an instantaneous pressure p in constant-rate operation as under such a pressure p in constant-pressure operation when the same volume of liquid is removed from the same amount of the original materials in both operations. Using this assumption, the changes of sample thickness and the expression pressure in the constant-rate process can be calculated with the analytical equation for the constant-pressure process. A useful graphical method is also shown for determining the change in expression pressure with time.