The precise assignments of cross polarization/magic angle spinning (CP/MAS) C-13 NMR spectra of cellulose I-alpha and I-beta were performed by using C-13 labeled cellulose biosynthesized by Acetobacter xylinum (A. xylinum) ATCC10245 strain from culture medium containing D-[1,3-C-13]glycerol or D-[2-C-13]glucose as a carbon source. On the CP/MAS C-13 NMR spectrum of cellulose from D-[1,3-C-13] glycerol, the introduced C-13 labeling were observed at C1, C3, C4, and C6 of the biosynthesized cellulose. In the case of cellulose biosynthesized from D-[2-C-13]glucose, the transitions of C-13 labeling to C1, C3, and C5 from C2 were observed. With the quantitative analysis of the C-13 transition ratio and comparing the CP/MAS C-13 NMR spectrum of the Cladophora cellulose with those of the C-13 labeled celluloses, the assignments of the cluster of resonances which belong to C2, C3, and C5 of cellulose, which have not been assigned before, were performed. As a result, all carbons of cellulose I-alpha and I-beta except for C1 and C6 of cellulose I-alpha and C2 of cellulose I-beta were shown in equal intensity of doublet in the CP/MAS spectrum of the native cellulose, which suggests that two inequivalent glucopyranose residues were contained in the unit cells of both cellulose I-alpha and I-beta allomorphs.