Vibration analysis of thick rotating cylindrical shells subjected to an initial pressure is described. The basic equations based on the Timoshenko type shell theory, including the effects of the initial tensions and resultant shear stresses due to rotation, torque, external pressure and axial compression load, are employed. By the modified Galerkin's method, frequency analysis is carried out for four boundary conditions (i. e., both ends (A) clamped with axial constraint, (B) simply supported without axial constraint, (C) simply supported with axial constraint and (D) clamped without axial constraint). Numerical results are compared with those based on the Flugge type shell theory and the difference between both theories is examined.