A polymer dispersion or solution containing a hydrophobic polysaccharide, which is dispersed or dissolved in liquid phase, and plasticizer composition of the polysaccharide, whereby at least 10% by weight of the plasticizer composition is formed from alkenyl succinic anhydride. The invention also relates to the preparation of polymer dispersions and solutions and to the films and coatings produced from them. The dispersions according to the invention are stable, and coating with excellent film-forming properties can be prepared from them.