Extracellular polysaccharides (EPSs) produced by algae can be applied in numerous branches of industry, depending on their origin and properties. In this work, the EPS produced with green microalgae Dictyosphaerium chlorelloides was studied by Fourier transformed infrared spectroscopy (FTIR) and atomic force microscopy (AFM), which enabled the characterization of its nanostructure. It was observed that the nanostructure of this exopolysaccharide self‐assembly depends on its concentration. At a concentration of 1 mg/mL the EPS formed a regular and porous matrix on mica, where fibers were cumulated in bundles of 50–70 nm wide. In a more diluted concentration of 10 μg/mL single molecules created a regular network with numerous branches. An average height of molecules was in the range of 400–800 pm with occasional local increase of the skeleton height which can be a result of an interconnection of the fibers. Analysis of the FT‐IR spectrum showed that the EPS has a structure of α‐glucan with the dominance of the galactose and rhamnose residues.