Normal mode superposition method for transient response analyses of layered poroelastic media was developed here. Normal modes here were complex due to the presence of the internal friction between the solid matrix and pore fluid. Orthogonality relations among the complex normal modes were established by using the symmetry of the governing equation. Transient response of layered poroelastic media is expressed by the convolution integral between Green's function and source function, and Green's function is represented in terms of normal modes which show the orthogonality relations. Numerical calculations were carried out to examine the effectiveness of the present method as well as the vibration properties of a poroelastic medium on a rigid base.