In this paper, the free vibration characteristics of orthotropic thin plates were investigated using improved Fourier series method (IFSM). The displacement functions of flexural vibration were expressed as an improved form of Fourier series, and the sine Fourier series was introduced to eliminate all the boundary discontinuities or jumps. The expansion coefficients of the displacement function were treated as the generalized coordinates, and determined using the RayleighRitz method. The results of orthotropic thin plates in different boundary conditions were presented and checked against the results published in the literature to demonstrate the efficiency and accuracy of the present method.