has given physical explanation of their observation in terms of the strik ing properties of soliton solution associated with the Korteweg-de Vries equation, which has been derived on a continuum model of the one-dimensional anharmonic lattice. At the same time, he has emphasized that the conventional approach of the phonon description is not a suitable way to examine the recurrence phenomena observed by Fermi, Pasta and Ulam. Although vve appreciate the remarkable successes of the soliton concept £or various kinds of the nonlinear wave phenomena,'1 we can not completely discard the phonon picture in the description of physical properties of crystals. It would be worth while examining interrelationship between the soliton concept and the phonon description of the anharmonic lattice. Therefore, we have undertaken to derive the Korteweg-de Vries equation for the interacting phonon systems vvithin the scheme , of quantum mechanical approach. Since the soliton describes nonlinear propagation of a finite amplitude wave in the classical treatment, we e2):pect that the correspond mg quantum mechanical state must be a state in which a large number of phonons are excited. In the following sections, we illustrate that the coherent state representation of the system 41 enables us to derive, the Korteweg-de Vries equation for the in teracting phonons. In order to establish explicit correspondence between Zabusky's continuum approximation and the coherent state description of phonons, we derive