We could prepare disk-shaped fibers without particular mechanical treatments from Eucheuma cottonii, the commonly used red algae for obtaining carrageenan. After carrageenan extraction from cottonii, the residues were bleached using chlorine dioxide and hydrogen peroxide. The morphology of the bleached fiber was disk-shaped one with a very thin fiber wall thickness of less than 100 nm and a diameter of approximately 100 μm. The sugar analysis and X-ray diffraction of the bleached fibers showed that they consisted of mostly glucose and had the same pattern as cellulose I with more than 50% crystalline structure, respectively. Compared to one-dimensional cellulose micro- or nanofibrils, which exhibits slow drainage and possess intolerably high drying energy, these two-dimensional disk-shaped fibers, when formed a layer in water medium, exhibit fast drainage and low drying energy. The formed sheet resulted in excellent transparency and high oxygen barrier property. Therefore, by using these disk-shaped, thin fibers from cottonii, we expect that the biodegradable and transparent oxygen barrier layer can be produced at a paper machine, which is, if possible, extremely difficult in the case of cellulose micro- or nanofibrils due to their slow drainage and high drying energy.