This study was carried out to investigate the variation of fiber tissues of some paper mulberies (Broussnetia kazinoki Sieb.). Every twig was selected for variation from 1 year old to 4 years old of the paper mulberies growing in Woensung, Bounghwa, Euiryung and Wanju in Korea. The results are summarized as follows: 1. The length and the width of fiber tissue increase to old twigs. 2. In primary fiber tissue the variation of length increases considerably slowly, but on the contrary that of width increases very rapidly. 3. In the secondary fiber tissue the variation of length increases comparatively rapidly but that of width does not. 4. In order to investigate the fact shown from the contrary results on the fiber length and width between primary and secondary fibers, the authors calculated the correlation, coefficient and the results show comparatively higher possitive correlation coefficient.