Localization of cellulose I alpha and I beta allomorphs was first characterized by electron micro-diffraction technique in 1991. The authors suggested that each allomorph localized alternatively along the microfibrillar direction. Later in 1998, from the similar but scrutinizing diffraction analyses, a mixed lateral / longitudinal distribution was suggested. The observation of enzymatic and acid hydrolysis of algal cellulose microfibrils, however, preferred the lateral localization of allomorphs, where I alpha moiety was covering the core I beta moiety. In this talk, the authors would like to review those previous findings and present new evidences on the distribution of I alpha and I beta in algal cellulose microfibrils, from the analysis of deuteration / rehydrogenation behavior at elevated temperature by FTIR technique.