The features of flocculation of kaolin suspension by samples of homopolymer poly-1,2-dimethyl-5-vinyl-pyridinium methylsulfate and its copolymers with acrylamide, N-vinylpyrrolidone and vinyl acetate have been studied. High activity of poly-1,2-dimethyl-5-vinylpyridinium methylsulfate due to the formation of sufficiently large aggregates at low doses of flocculant was shown. It is also revealed that the synthesized copolymers and terpolymers in comparison with homopolymer have higher flocculating activity, which is characterized by a higher degree of suspension clarification. The reasons for the high flocculation activity of copolymers are related to the specific content and distribution of cationic centers in macromolecules. Additionally polyelectrolytes were investigated as dewatering agents in activated sludge treatment. The obtained results allowed to recommend the use of pyridinium polyelectrolytes as flocculants in the processes of water treatment of various origins.