Abstract: Based on the micromechanics, a general method of determining the elastic constants of trans-versely anisotropic composites is proposed. For long-fiber reinforced composites, the Young's modulus, the two transverse elastic moduli, the shear modulus and the Poisson's ratio are determined by this method, which demonstrates the applicability and the accuracy of the present method, as an analytical approach for the esti-mation of material properties. This is a typical example for the study of composites mechanics, related with the micromechanical method.