The main goal of the work was to examine the structural changes induced by water (D2O and H2O) in the dense cellulose him, Tomophan I, using temperature time-resolved SAXS and WAX measurements. We found that dry cellulose and water-saturated cellulose contains hydrophobic microregions at room temperature. At increasing temperature microphase separation was observed, as a formation of a broad peak on the SAXS curves, with T-c of about 55 and 60 degrees C, depending on the kind of water. Further heating, up to 85 degrees C, causes an appearance of a set of very small peaks, generated by the cubic structure, in SAXS. The structural changes of the system are typical for the thermo-associative process, observed in the copolymer-water systems.