A method has been developed to predict the damping behavior of an equivalent plate formed from sandwich panels with a thermoviscous fluid core, which is based on an asymptotic approach. The technique works on the break-up of the basic physical quantities such as pressure, temperature, and particle velocities as constants and linear functions of the z coordinate, which signifies the perpendicular direction from the plate mid-surface. The asymptotic modeling is performed in a very thin and highly thermoviscous fluid layer on the full set of linearized Navier Stokes equations. The use of highly viscous fluid layers such as Rhodorsil® 47 oils, yields high damping loss factors, which are of the order of 10−1 . The effects of the panel thickness and the fluid core thickness are also studied. It is shown that the damping loss factor of the equivalent plate is independent of the frequency. Experimental validation provides a good agreement with the theoretical results.