The invention relates to the field of medicine, in particular to novel peptides having biocidal properties, more particularly antibacterial, antifungal and antiviral properties, and preparations based thereon. Proposed are a biocidal peptide of general formula Y-Ile-Leu-Pro-X-Lys-X-Pro-X-X-Pro-X-Arg-Arg-NH2, where X is 4-nitrophenylalanine; 4-chlorophenylalanine; 4-methoxyphenylalanine; D-phenylalanine; 4-aminophenylalanine; 4-aminobenzoylphenylalanine; homophenylalanine; 4-tertbutylphenylalanine; 2-methylphenylalanine; 4-fluorophenylalanine; pentafluorophenylalanine; or 2-trifluoromethylphenylalanine; and Y is H or palmitoyl or aminodecanoyl, and a preparation in the form of a gel with biocidal properties, containing, as an active substance, said peptide at a concentration of 0.001 to 0.1 wt%. The claimed peptides demonstrate biocidal properties towards bacteria, including spore-forming bacteria, mould fungi, and also viruses. The peptide-based gels can be used for treating bacterial and viral infectious diseases and infectious comorbidities.