Coagulation step in conversion of milk into cheese plays a decisive role in contributing textural qualities to the cheese. During coagulation, milk changes its state from liquid to semisolid known as gel or coagulum. This accompanies changes in such physical properties as density, firmness and viscosity. In this research, an ultrasonic method was diveloped as a nondestructive method to study the milk coagulation process. The ultrasonic pulse-transmission method was used to calculate the ultrasonic velocity and attenuation when wave passed through milk. During coagulation, density of milk and ultrasonic velocity without obviously changes but the shear viscosity and wave diffusivity of milk increased; and the bulk viscosity of milk and ultrasonic attenuation decreased.