Although the high crystallinity of cellulose fiber is well known, ¹ its dichroism in the infrared region has not been examined, to the best of the author's knowledge. Recently, the author observed the infrared absorption spectra of oriented cellulose fibers using polarized radiation. The results support the previously postulated crystal structure of cellulose with a little modification, and also lead to assignments of some of the observed bands. The results are particularly interesting because they indicate the arrangement of the hydrogen-bonded OH groups, which is not directly known by other methods. The experimental results and their interpretations will be described in this paper.