Abstract: Based on the framework of Tandon and Weng,the elasto-plastic theory of an orthotropic composite reinforced with unidirectionally-elliptic aligned cylinders,and a transversely isotropic composite reinforced with two-dimentional randomly-oriented elliptic cylinders,is established.The secant moduli yield surfaces and the average stress concentration factory of the matrix are derived.It is shown that both the secant moduli and the yield surfaces are strongly influenced by the shape of fibers;ribbons are seen to be most effective in transversly isotropic composite.