Free vibration of rotating rectangular plates with an exponentially varying thickness is studied. The plate is clamped at the rim of a central hub and is free along the other three edges. In the general formulation, the plate is considered to be made of orthotropic materials. The differential equations governing the in-plane displacements before vibration takes place are solved by a finite difference method. The curve-fitted previbratory in-plane stress distribution based on the numerical results is used in the equation for the flexural vibration of the plate, and the natural frequencies are subsequently determined by the extended Galerkin procedure. Some numerical results are presented for illustrative purposes.