The crystallite sizes of ramie fibers treated with caustic soda of various concentrations with and without constraints were measured by X-ray diffraction method. The dimenisons of the crystallites on the 040 plane monotonously decreased as the concentration of caustic soda increased in the samples treated under constraint, whereas they suddenly decreased in the sample treated by the 2N caustic soda without constraint. And the dimensions of the crystallites on the 002 plane showed similar decrease both with and without constraints, except that they slightly increased by treating in the 8N caustc soda without constraint. It may be concluded that ramie cellulose can be supposed to be fully extended molecular chains, and that recrystallization occurs in the solution of high alkali concentration without constraint.