Halomonas ventosae RU5S2EL, a halophilic Gram-negative bacterium isolated from salt sediments of lake Elton (Russia), was cultivated and the lipopolysaccharide was extracted by the Westphal procedure. The O-specific polysaccharide (OPS) was obtained by mild acid hydrolysis of the lipopolysaccharide and was studied by sugar analysis along with 1 H and 13 C NMR spectroscopy, including 1 H, 1 H COSY, TOCSY, ROESY, 1 H, 13 C HSQC, and HMBC experiments as well as Smith degradation. The OPS was found to consist of branched pentasaccharide repeating units of the following structure:Image 2