Dissolution of cellulose in aqueous hydroxide offers a procedure for regeneration of cotton or wood celluloses. The aqueous NaOH system for dissolving cellulose seems to have considerable potential for fiber production and also as a medium for preparing cellulose derivatives. Reactions with phosphoric and phosphorous acids, phenyl-and phenoxy phosphonic dichlorides, and an amido phosphite oligomer on aqueous dissolved cellulose are described. The resulting products are characterized by analytical and spectral methods (infrared and X-ray diffraction) to determine phosphorus and nitrogen content, substitution degree, and polymerization degree. Particular attention was given to the effects produced by chemical modification on the crystalline pattern of microcrystalline cellulose. Some remarks are also made about the thermooxidative behavior of phosphorylated cellulose.