The time evolution of concentration profiles in binary multilayers is studied by use of the Cahn-Hilliard equation on the basis of the lattice gas model. The profiles in the relaxation process to the thermal equilibrium state are numerically calculated for cases with bulk ordered structures. It is found that the appearance and disappearance of antiphase boundaries play the most important role in the relaxation process. If the boundaries are not found or disappear rapidly with time, the system attains the equilibrium state in a very short time. If not so, however, it takes a very long time. In addition, the role of the surface in the relaxation process is discussed.