Fluid diffusion in fiber reinforced composites is typically anisotropic. Diffusivity in the fiber direction is faster than in the transverse direction. The reason for this behavior is not yet fully understood. In this work, dealing with glass fiber epoxy composite immersed in distilled water, an experimental procedure for determination of anisotropic diffusion constants from a laminate is presented. The method has the advantage that it does not require sealing of the samples edges because 3-D anisotropic diffusion theory is implemented for obtaining the diffusion constants. A microscale model is presented, where matrix and fiber bundles are modeled separately. The matrix properties have been obtained experimentally and the fiber bundle properties have been deduced by the composite homogenized diffusivity model. The analysis indicates that the anisotropic diffusion of the composite is due to inherent anisotropic properties of the fiber bundles.