The present invention relates to a use of a copolymer comprising N-vinyllactam, and vinylimidazol or a quaternized vinylimidazol in polymerized form as dispersing agent in an aqueous composition containing a water-insoluble pesticide. Further on, it relates to an aqueous composition which contains a copolymer comprising in polymerized form at least 20 mol% N-vinyllactam, and at least 1 mol% vinylimidazol or a quaternized vinylimidazol, a water-insoluble pesticide, and a dissolved salt. The invention also relates to a method for preparing the said composition by mixing water, the water- insoluble pesticide, the salt and the copolymer.,Another subject is a method for controlling phytopathogenic fungi and/or undesired plant growth and/or undesired attack by insects or mites and/or for regulating the growth of plants, where said composition is allowed to act on the particular pests, their habitat or the plants to be protected from the particular pest, the soil and/or on undesired plants and/or the useful plants and/or their habitat.