In the present study, stress analysis of fiber reinforced thin composite shafts subjected to unbalance excitation and steady torque, is carried out. Shafts of uniform as well as variable wall thickness are considered. The shaft is modeled as a simply supported Timoshenko beam in which shear deformation, rotary inertia and gyroscopic effects have been included. Modified equivalent modulus beam theory has been adopted. Rayleigh-Ritz displacements are used for deriving the solution equations. Shafts with a uniform wall thickness, and with variable wall thickness in which the thickness is varied along the axial length of the shaft for three different cases of fiber angles have been studied. Axial variation of stresses is studied in detail. Results obtained indicate that the stresses in the variable wall thickness are smaller than the one with uniform wall thickness, even for the same weight of the shaft. © 2000 OPA (Overseas Publishers Association) N.V.