Modal properties of viscoelastically damped plates that were clamped at the edges between sandwich rectangular frames were obtained by FEM analysis and modal strain energy analysis. The modal damping loss factors were calculated at various temperatures using the reduced-temperature nomogram of the applied damping material obtained from the measurements based on the Oberst beam test method. Modal frequencies and loss factors of test plates were measured by the half-power bandwidth method in a thermostatic chamber and were compared with the analytical results. There are small differences of the modal frequencies between the analytical and experimental values. The differences are assumed to be due to the boundary condition at the interface of plate and frames. The loss factors show good agreement for plate modes. The vibration of the point-exited plates was calculated using the modal properties. The transfer functions between the applied forces and the vibration responses were compared with measurements. Finally, the radiated sound field was evaluated from the vibration responses by BEM analysis, and acoustical intensity measurements were carried out at the surface of the plates. Mean-square velocity and radiated sound power vary inversely as loss factor.