For the assignment of C-13 resonance for C2, C3, and C5 of cellulose IIII, C-13-enriched celluloses were biosynthesized by Acetobacter xylinum (A. xylinum) ATCC 10245 in the culture medium containing D-(2-C-13), D-(3-C-13), or D-(5-C-13)glucose. After the C-13-enriched celluloses and Cladophora cellulose were converted into IIII allomorph by the ethylenediamine treatment, cross-polarization/magic angle spinning (CP/MAS) C-13 NMR spectra of these cellulose IIII samples were measured. By comparison of the CP/MAS C-13 NMR spectrum of Cladophora cellulose sample with those of the C-13-enriched celluloses, C-13 resonance lines of the cellulose IIII were completely assigned for the first time. As a result, all carbons of cellulose IIII were shown in singlet in the CP/MAS spectrum of cellulose IIII, which suggests that cellulose IIII is made up of one kind of glucopyranose residue.