We have previously reported a novel Fourier transform infrared (FTIR) method for evaluating both the accessibility and lateral dimensions of cellulose microfibrils. This method differs from conventional deuteration in that the OH groups in the crystalline region were initially completely deuterated. The samples were then rehydrogenated by immersing them in water at 25 C, during which only the OD groups on the surface were rehydrogenated. The ratio of OD to OH groups measured for cellulose from various origins was used to estimate microfibril dimensions, which were compared with the data from X-ray diffractometry. The rehydrogenation process was further investigated by immersing the deuterated samples in water at elevated temperatures. The behavior of rehydrogenation under heat treatment was converted to observe the microfibril shape, which was in good agreement with the cross-sectional images obtained by diffraction contrast transmission electron microscopy techniques.