An analytical model for the free vibration of non-uniform, anisotropic, thin-walled wind turbine blade is presented. The blade is constructed from laminated fibrous composite materials with variable thickness and stiffness. The study focuses on the blade spar that represents the main supporting structure within a wind turbine blade. Two specific lay-up configurations; namely, Circumferentially Asymmetric Stiffness (CAS) and Circumferentially Uniform Stiffness (CUS) are analyzed. The transfer matrix method is used to study the vibration behavior of a tapered spar by dividing it into multiple uniform segments, each of which has different length, cross sectional dimensions and material properties. The influence of coupling on the vibration modes is identified and the functional behavior of the frequencies with the lamination parameters is thoroughly investigated and discussed.