The inventions relate to antiseptic agents and the method for producing thereof and can be used as a broad-spectrum disinfectant in medicine, veterinary medicine, agriculture etc. The method for producing of biocidal polyguanidine that comprises condensation polymerization of hexamethylenediamine with guanine salt additionally uses hydrazine hydrate during the condensation polymerization process, at the following ratio of components, mass % : Biocidal polyguanidine obtained by means of the abovementioned method, with the following formula : or where n - the number of links A in a single unit of the polymer chain, n = 1 - 3; m - the number of links B in a single unit of the polymer chain, m = 2 - 10; z - the number of single units in the polymer chain, z=4-20; Acid - an acid. The inventions allow obtaining a biocidal polyguanidine with high level of broad-spectrum antimicrobial activity.