The intestinal diseases of bacterial aetiology are characterized by high prevalence and a severe course, especially at a young age, concomitant immunity suppression or chronic diseases of the gastrointestinal system. Therefore, it is expedient to search for the new antimicrobial drugs, and it seems promising to use known antimicrobial agent decamethoxinum for the development of peroral medicinal forms, such as “Decasan” that is 0.02% decamethoxinum solution for peroral use worked out by “Yuria Pharm.” This study aimed to determine the parameters of acute toxicity of decamethoxinum substance and “Decasan,” as well as to study the possible toxic effects of the latter in chronic administration. The experiments on rats have shown that “Decasan” at the maximal allowable dose of 20 ml/kg does not cause lethality in rats. For decamethoxinum substance LD50 equals 586 (484:588) mg/kg in intragastric administration, corresponding to the IV class of low toxic substances (500 mg/kg