Free vibrations of rotating disks are investigated by using the Galerkin method. An approximate function which satisfies the boundary conditions and normalizing constraint is chosen. The different boundary conditions are also investigated in order to understand the vibrational characteristics of this type of structures. The stress distributions on the rotating disk with different boundary conditions are used in the analysis. The effects of rotation speed on the natural frequencies are studied. The results are presented in tables and figures and also compared with the results given in the literature.