This paper deals with nonlinear liquid surface and interfacial wave motions in a tank containing two incompressible irrotational fluids of different densities. In order to investigate time history responses and nonlinear characteristics, we apply canonical equations (Hamiltonian equations) to this problem. The time histories and the transitions of surface and interfacial wave motions are given by solving the canonical equations of this system. This study is intended to clarify the nonlinear coupling characteristics for this system. We have focused on the N -Wave Resonant Interaction (NWRI) and investigated occurrence conditions of the NWRI. In particular, the time history responses on the resonant state caused by the Three-Wave Resonant Interaction (3WRI) are discussed for the rectangular and the circular cylindrical tanks. On the other hand, the validly of the theoretical analysis is verified through the experiments. These results are in good agreement with each other.