The crystallinity, crystallite sizes and orientation of hemp fibers treated in caustic soda of various concentration with and without constraint were measured by wide angle X-ray diffraction method. It was found that, 1) The crystallinity monotonously decreased with the increase of caustic soda in the samples treated with constraint, whereas it decreased and again increased with the increase of alkali concentrations in the samples treated without constraint. 2) Crystallite sizes of 002 plane decreased with increase of alkali concentrations, more remarkable decrease occured in the samples treated with constraint, And there were no significant changes on the crystallite sizes of 040 plane in the samples treated with and without constraint. 3) The orientation increased in the samples treated with constraint, whereas it decreased in the samples treated without constraint. The foregoing observations indicate that it is advisible to avoid high alkali concentration and excess tension.