Lipopolysaccharide was obtained by hot aqueous-phenol extraction from Vreelandella alkaliphila B521, a moderately halophilic gram-negative bacterium isolated from mud of Lake Botkul, Volgograd Region, Russia. The O-polysaccharide (OPS) was released by mild acid hydrolysis of the lipopolysaccharide and was structurally characterized by chemical analyses and by 1D and 2D NMR spectroscopy. The following structure of the OPS trisaccharide repeating unit was identified: →4)-α-l-GulpNAcA-(1 → 4)-α-l-GulpNAcA-(1 → 6)-α-d-GlcpNAc-(1→.