The test samples prepared from Yucca leaf of filamentosa species, which was divided into 5 different stages of growth, was prepared by boiling and dipping treatment of the sample in thin purpose to investigate the possible utilization of Yucca cellulosics as a textile fiber. The fiber yield structure and various physical properties of the fiber treated with 6 different concetrations of NaOH (4%, 8%, 12%, 15%, 17%, 20%) after eliminating cuticle and chlorophyl, were investigated and revealed in the followings. 1. It was indicated that cellulose yield was increased with increasing stage of growth of Yucca leaf. 1 2. When fiber bundle after boiling and dipping treatment was contacted with different concentsration of alkali, the amount of cellulose yield, lignin and pentosan were decreasing, especially decreased residual pentosan was peculiar. 3. Microscopic structure showed that the single fiber of alkali treated was closely adjacent comparing to that of untreated fiber, and also showed the plain surface of it. Cellulosic fiber bundle treated with high concentration of alkali was substancially divided into single fiber. 4. X-ray diffraction showed that Yucca cellulose from Yucca cellulosics is exactly the same cellulose as the ordinary fiber cellulose. Crystallinity of cellulose, size and orientation of the crystallite were increased with increasing stage of growth of Yucca cellulosics, and reversely they were decreased with increasing concentration of alkali treatment.