Constrained layer damping can be an effective method to control transverse vibration of thin structures. The commonl used equation of motion governing the behavior of constrained layer damped Euler-Bernoulli beams, originally derived b Mead and Markus (1969), does not account for the relative transverse motion between the constraining layer and the base beam. When a soft viscoelastic layer or a stiff constraining layer is used, this relative transverse motion may become significant. To account for this motion, Miles and Reinhall (1986) developed a model that included the thickness deformation of the viscoelastic layer. The purpose of this paper is to demonstrate the existence of the thickness deformation through experiments and to investigate the validity of the Miles and Reinhall model. Experimental results show that the thickness deformation is significant in the high frequency range, and that the inclusion of the thickness deformation improves the accuracy of the analytical model.