Abstract: In order to predict and suppress delamination in composite laminates,a comprehensive knowledge about the mechanism of interlaminar stresses in compasite laminates is necessary. In the present paper, a nonlinear quasi-three-dimensional finite element procedure is presented,in which a mpdified Elahn-Tsai nonliner constitutive equation is used.The results for an angle-ply ±45_s and symmetric cross-ply laminates are presented. The lamina properties in the laminates have obvious nonlinearity in shear deformation and a little in transverse tension.Emphasis is placed on assessing the stress behavior in the regions close to ply-interface and exposed free edge.Compared with elastic results,the solutions indicate that material nonlinearities can cause the decrease in interla minar shear stresses to a certain degree,but they have little effect on the distributions of interlaminar normal stress.