It is well known that cotton fibers are sensitive to moisture. The interactions of cellulose chains and water molecules could therefore have an influence on the fiber properties. In this presentation, we will investigate the effect of adsorbed water on the specific surface area of standards cotton fibers. The amount of adsorbed water was determined by Thermogravimetric analysis. Adsorption of methylene blue in aqueous phase was used to measure the surface specific area. A numerical relationship of the form S_BM =a +b X has been obtained, where S_BM represents the specific surface area, X the percentage of adsorbed water, a and b are experimental constants.