A comparative study of the reactivity of cellulose with different supramolecular structures (bacterial, regenerated, cotton cellulose) in oxidation by nitrogen (IV) oxide solutions in chloroform is performed. Using IR spectroscopy, elemental analysis, titrimetry, X-ray diffraction, and electron microscopy, the effect of oxidizer concentration (10–40%) and reaction time on the composition of modified cellulose, the degree of swelling, morphological features of the fibrous network of films, and the rate of degradation in vitro are studied. Conditions for obtaining gel films of oxidized bacterial cellulose with the content of carboxyl groups in the range of 1.6–25.6% and a degree of water absorption of 160–6340% are optimized. It is shown that as the content of carboxyl groups increases, the hydrolytic stability of oxidized bacterial cellulose decreases sharply: gel films with a content of carboxyl groups in the range of 13.5–24.8% degrade over a period of three days.