The physicochemical properties of the complex exopolysaccharide ethapolan (EPS) produced by Acinetobacter sp. 12S during growth on media with various C/N ratios and different concentrations of mineral components and phosphate buffer were studied. Irrespective of the cultivation conditions, the concentrations of carbohydrates (38-44%) and pyruvic acid (3.2-3.7%) in the total EPS, as well as in the acylated (AP) and non-acylated (NAP) polysaccharides obtained from them, were practically the same. The EPS, AP, and NAP were also identical in their monosaccharide composition: the molar ratio of glucose, mannose, galactose, and rhamnose was 3 : 2 : 1 : 1. The polysaccharides contained different concentrations of mineral salts (6-28%), uronic acid (3.7-22.0%), and fatty acids (5.8-15.4%); they also differed in the ratio of acetylated and nonacetylated polysaccharides. Due to the differences in the chemical composition and molecular mass (500 kDa - 1.5 MDa), the viscosities of the EPS solutions (in the presence of 0.1 M KCl, in the H(+)-form, and in Cu(2+)-glycine system) were different as well.