The present study demonstrates that interfacial acoustic waves can be excited at the interface between two phononic crystals. The interfacial acoustic wave between two phononic crystals is analogous to the surface electromagnetic wave between two photonic crystals. While past works on phononic crystals exploit the unique bandgap phenomenon in periodic structures, the present work employs the Bloch wave in the stop band to excite interfacial acoustic waves that propagate along the interface and decay into both media. As a result, the interfacial wave can be employed in an effective wave filter in which the incident acoustic wave energy is guided by the interfacial wave to the lateral direction; thus, its propagation in the normal direction is inhibited. The advantage of using two phononic crystals is to excite the interfacial wave even at normal incidence.