The vibrational modes localized at a superlattice-liquid interface are studied theoretically. We calculated the phonon transmission rate and found the peculiar peak due to the interface-localized mode. The magnitude of this peak is governed by the number of constituent bilayers (N) of superlattice. We derived the equation determining N = N-max for which the transmission rate takes the maximum value for a given combination of the superlattice and liquid. When N = N-max, the interface-localized mode has the same feature inside the superlattice as the surface-localized mode generated in the semi-infinite superlattice. (C) 2002 Elsevier Science B.V. All rights reserved.