Abstract: A theoretical analysis is presented for the postbuckling behaviour of simply supported orthotropic rectangular Plates subjected to combinedo in-plane biaxial compression and edge shear,By perturbation technique and selecting the perturbation parrrieter relating to the maximum deflection,the nonlinear coupled partial differential epuations are reduced to a system of uncoupled linear partial differential equations and then salved by using the double Fourier series method.Numerical results are obtained for glass-epoxy composite plates,The effect of aspect ratio and loading parameter on the postbuckling behaviour is illustrated graphically and discussed.The numerical results show a good convergence of the present solution and they are in good agreement with the available data.