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Crystalline structures of cellulose (named as Cell 1), NaOH-treated cellulose (Cell 2), and subsequent CO₂-treated cellulose (Cell 2-C) were analyzed by wide-angle X-ray diffraction and FTIR spectroscopy. Transformation from cellulose I to cellulose II was observed by X-ray diffraction for Cell 2 treated with 15–20wt% NaOH. Subsequent treatment with CO₂ also transformed the Cell 2-C treated with 5–10wt% NaOH. Many of the FTIR bands including 2901, 1431, 1282, 1236, 1202, 1165, 1032, and 897cm⁻¹ were shifted to higher wave number (by 2–13cm⁻¹). However, the bands at 3352, 1373, and 983cm⁻¹ were shifted to lower wave number (by 3–95cm⁻¹). In contrast to the bands at 1337, 1114, and 1058cm⁻¹, the absorbances measured at 1263, 993, 897, and 668cm⁻¹ were increased. The FTIR spectra of hydrogen-bonded OH stretching vibrations at around 3352cm⁻¹ were resolved into three bands for …