A polysaccharide isolated after mild acid degradation of the lipopolysaccharide of Vibrio vulnificus clinical isolate YJ016 was found to contain L-Fuc, D-GlcpNAc, 2,4-diacetamido-2,4,6-trideoxy-D-glucose (di-N-acetylbacillosamine, D-QuiNAc4NAc), and 2-acetimidoylamino-2-deoxy-L-galacturonic acid (L-GalNAmA). The last sugar derivative was confirmed by correlations for nitrogen-linked protons in 2D TOCSY and ROESY spectra measured in a H(2)O-D(2)O mixture. The following structure of the polysaccharide was established by (1)H and (13)C NMR spectroscopy, including 2D ROESY and (1)H,(13)C HMBC experiments: [structure: see text], where the degree of 6-O-acetylation of the lateral beta-GlcNAc residue is approximately 70%.