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Abstract Background Shigella spp. are Gram-negative intracellular pathogenic bacteria belonging to the family Enterobacteriaceae and can cause bacterial dysentery, a severe diarrheal disease. The pathophysiological impact of the Gram-negative bacteria is highly related to the composition and structural variability of lipopolysaccharides, the major lipoid components of the outer membrane. Out of the 114 genes involved in the lipopolysaccharide biosynthesis pathway, 47 genes are specific to Shigella spp. Changes in the specific genes can lead to loss of the O polysaccharide side chain, resulting in rough (R) type bacteria with increased sensitivity to temperature, or hydrophobic antibiotics. The formation of various different lipopolysaccharides or lipooligosaccharides has been observed previously in a mutant line showing altered biological properties, but the genetic background has not been investigated in detail. Results The parental strain of the mutant line, Shigella sonnei 4303, was subjected to whole genome sequencing to gain a better insight into the structure and biosynthesis of lipopolysaccharides. The sequencing revealed a 4,546,505 bp long genome including chromosomal and plasmid DNA, and the lipopolysaccharide biosynthesis genes were also identified. A comparison of the genome was performed with the phylogenetically closely related, wild type, well characterized, highly virulent strain, S. sonnei 53G. Conclusion Analysis of the lipopolysaccharide biosynthetic genes helped us to get more insight into the pathogenicity and virulence of the bacteria. The genome revealed high similarities with S. sonnei 53G, which can be used as a standard in characterizing the S. sonnei 4303’s R-type isogenic derivatives.