To obtain the subject composition having high dispersion stability in an aqueous solvent, effectively usable over a long period and useful for imparting antimicrobial properties to a water-based coating, a coating agent, a wall material, etc., by including a specific salt of an anionic hydrophilic polymer.

This composition is obtained by including a mixed salt of (B) an alkali metal salt (preferably a sodium salt) of (A) an anionic hydrophilic polymer which is preferably a water-soluble homoglycan (preferably a carboxymethyl group-containing cellulose, etc., having <1.5 degree of substitution of the carboxymethyl groups per anhydroglucose unit) with (C) a quaternary ammonium salt having antimicrobial properties (e.g. benzalkonium chloride). The formation ratio of the salt based on 1 mol of anionic groups in the ingredient A is preferably about 70-100% and the molar ratio of the ingredients B/C is preferably about (0.4/0.6) to (0.6/0.4).