The O-specific polysaccharide from Escherichia coli O113 lipopolysaccharide was separated from the core and lipid A by mild acid hydrolysis and purified by GPC. Methylation analysis and H-1 and C-13 NMR spectroscopic studies of the O-deacetylated polysaccharide allowed the determination of the structure of the pentasaccharide repeating unit of the polysaccharide which can be written as [GRAPHICS] The position of the O-acetyl groups was not determined.