The diffusion of water into unidirectional Kevlar fibre reinforced epoxy resins was studied as a function of fibre orientation and, for unidirectional (0°) composites, as a function of volume fraction (Vf). As the angle increased from 0 to 90°, the diffusivity increased dramatically; i.e. as more and more fibre-ends were exposed to the shorter diffusion path, the diffusivity increased. The equilibrium weight gain of water (M∞) in the composites increased with theVf of the fibre. M∞ of Kevlar fibre was calculated to be 4.9%. At a constantVf, specimens of the same thickness and width but different lengths were used to determineD22, the diffusion coefficient of the composite along the fibre, andD22, the diffusion coefficient transverse to the fibre. The initial data for the percentage weight gain against the square root of time were non-linear, which was attributed to the anisotropy of the diffusion process. The anisotropy arises from the much higher value ofD11 as compared toD22. AsVf increased from 0.37 to 0.59,D11 increased from about 0.83 to about 4.2 × 10−12m2 sec−1, whereasD22 decreased from 0.21 to 0.033 × 10−12 m2 sec−1. Thus, the ratioD11/D22 increased from 3 to over 100 as U increased. The experimental sorption data could be fitted satisfactorily with these diffusion coefficients.