A semi-analytical finite element analysis is presented for determining the natural frequencies of thin circular isotropic cylindrical shells with variable thickness. Love's first approximation shell theory is used to solve the problem. The effect of thickness distribution on natural frequencies was determined for two boundary conditions; viz., simply supported-simply supported and clamped-clamped with different length to radius ratios. The thickness distribution was assumed to be linear and quadratic along the axial direction. © 1991.