This paper gives a method to represent interaction between elastic objects for medical VR simulation. To simulate collisions of multiple organs is indispensable for realistic deformation and haptic display. The interaction model defines displacements of colliding elements based on normal stress. The proposed model not only prevents unrealistic overlap of the objects, but also produces accurate deformation and force feedback considering stiffness of the objects. A prototype simulator of rectal palpation is constructed for evaluation of the proposed model. The results of experiments confirmed the method expresses organ-organ interaction in real time, and provides realistic and perceivable force feedback.