Our recent IR study demonstrated that hydrogen-bond structure in cellulose I beta drastically changes around 220 degrees C (Watanabe et al. Biomacromolecules 2006, 7, 3164). In the present study, temperature-dependent IR spectra of cellulose la from 30 to 260 degrees C were analyzed by use of perturbation-correlation moving-window two-dimensional correlation spectroscopy. It was observed that as in the case of cellulose I beta abrupt changes in the hydrogen-bond structure occur around 220 degrees C in cellulose I alpha It was also revealed that although weakly hydrogen-bonded OH groups in 10 are stable below 230 degrees C thermal oxidation of those in I alpha is accelerated around 220 degrees C. In this way, the present study has clarified a difference between the thermal behavior of lot and that of I beta at the functional group level. Our result suggests that the drastic change in the hydrogen-bond structure around 220 degrees C makes cellulose la much more unstable than I beta.