The bacteria of Thiobacillus thioparus and Stenotrophomonas maltophilia are capable to form a thick biofilm complicated as to its structure on the surface of low-carbon steel. This biofilm formation on any surface occurs under the adhesion of the cells of the plankton growth model with the help of synthesis of muciferous exopolymers with adhesive properties. Hence the monosaccharide composition of the exopolymer complex in the form of polyol acetates was studied by chromate-mass-spectrum method. A significant difference in the composition of exopolymer monosaccharides with the presence of steel model in the medium and without it was established; a change in the monosaccharide composition of mono- and binary culture in the conditions of plankton and biofilm growth was also observed.