Abstract: This paper proposes a BEM computation model to calculate the transverse effective moduli and Poisson's ratios of unidirectional fiber reinforced composites.The computation results of ν₁₂,ν₃₂,ν₁₃ and ν₂₃, are in good agreement with the experimental results.The E₂,E₃ for carbon-fiber reinforced composites coincide with the experimental results excellently.However,for glass-fiber reinforced epoxy composite,the computation results of E₂,E₃ are about 10-25 percent lower.For the latter,it is guessed that there may exist remarkable interlayer effect,which was not considered in the computation process.