Abstract: A theoretical approach is presented for analyzing thein-plane mechanical properties of the stitched composite laminates based onthe microstructures of fibers near the stitch holes. The geometricalcharacteristics of the distorted fibers in the stitch unit cells areconsidered. The elastic constants and stiffness matrices of lamina andlaminate are obtained finally. The effects of stitching parameters on theequivalent elastic modulus of the laminates are studied using the finiteelement analysis. The results show that the material properties of stitchedcomposite laminates are inhomogeneous due to stitching, and theequivalent elastic modulus of the laminates decreases with the increase ofthe stitch density and thread diameter.