Stator end windings of large turbogenerators are subjected to static and harmonic forces due to electromagnetic interaction of the electric currents in them. In this paper the free vibration characteristics of these end winding coils are analyzed by using a transfer matrix approach, with account taken of the flexural and torsional rigidities of the composite coil section. An analytical method in which Prandtl's stress function and Roth's double infinite series are used is developed for determining the effective torsional rigidity of the composite rectangular sections with jump non-homogeneity along the principal directions of the section. The necessary equations for the space curve representing the end winding coils are developed. The natural frequencies of a single coil have been experimentally determined by an impact hammer test. The theoretical and experimental values are in good agreement.