In this paper, the free vibration of rotating laminated composite beams (LCBs) with general layups and single through-the-width delamination is analytically investigated. The Hamilton's principle is used to derive the coupled governing di®erential equations and boundary conditions for the rotating delaminated beam, considering the e®ects of shear deformation, rotary inertia, material couplings (bending-tension, bending-twist and tension-twist couplings), and Poisson's e®ect. Both the free mode and constrained mode assumptions are adopted. Analytical solution for the natural frequencies and mode shapes are presented by incorporating the constraint conditions using the Lagrange multipliers method. The accuracy is assured by the convergence of the natural frequencies, as well as by comparison with published results. The e®ects of various factors such as delamination parameter,¯ber angle, hub radius, material anisotropy, end mass and rotating speed are studied in detail. The di®erence between the results based on the free mode and constrained mode assumptions is also investigated.