The biodegradability of cellulose fibers was evaluated by employing a toil burial test, an activated sewage sludge test, and an enzyme hydrolysis. The surface changes after biodegradation were observed by optical microscopy. From X-ray (diffraction analysis (XRD), the changes in the specimen crystallinity and internal structure as a result of degradation were a1so investigated. The biodegradability decreased in the following order: rayon > cotton 》 acetate. Rayon fibers, which have a low degree of crystallinity and a low degree of orientation, showed the highest biodegradability. However. In spite of its low crystallinity, acetate tubers exhibited very low biodegradability due to the presence of hydrophobic groups in its strurture. Linen showed an inconsistent behavior in that it had the highest biodegradability in the soil burial refit, but a lower biodegradability than that of cotton In the activated sewage sluge test. Therefore, it is expected that there are additional factors such as noncellulose com ponents that influence the biodegradability of the cellulose fibers. The colors of degraded specimens turned brown, black, and blue flue to fungal growth. XRD revealed a sligh1 increase in the crystallinity of linen. cotton and rayon fibers at the initial stage. but a continuous decrease thereafter. In conclulion. the biodegradability of cellulose fibers was closely correlated to the moisture regain of the fibers, which reflects the hydrophilicity and internal structure of the fibers.