Аннотация:The substance of niclosamide (NCS) is part of anthelmintic and anticancer drugs, its disadvantage is its poor solubility in water and physiologically active media, which leads to its knowingly high dosage to achieve a therapeutic effect, increased cost and increased drug toxicity. To improve the solubility of the NCS’ substance, its mechanochemical modification with the use of polymeric substances was proposed, which made it possible to increase this indicator up to 40-52 times. Such an increase in solubility did not adequately affect the change in cytotoxic activity. Judgments about the selectivity of this activity with respect to various tumor cultures are given.