Abstract: The three-dimensional finite element method (FEM) was combined with me-somechanics to determine the local and average stress-strain fields of fibrous composites. Computations for the circle and non-circle fiber-reinforced composites were performed to examine the effects of micro structures on the effective properties. The results indicate that the axial Yang's modulus is insensitive to the microstructures while the fiber distributions or fiber arrays as well as fiber shapes significantly affect the transverse effective properties of the composites.