Peptides having, as constitutive amino acids, (1) 4 glutamine residues, 1 glutamic acid residue, 1 serine residue, 2 valine residues, 1 isoleucine residue and 5 leucine residues, and having a 3-hydroxydecanoyl group bonded, via an amide linkage, to the N-terminal leucine residue thereof; (2) 4 glutamine residues, 1 glutamic acid residue, 1 serine residue, 3 valine residues, and 5 leucine residues, and having a 3-hydroxydecanoyl group bonded, via an amide linkage, to the N-terminal leucine residue thereof; or (3) 4 glutamine residues, 1 glutamic acid residue, 1 serine residue, 2 valine residues, 1 isoleucine residue and 5 leucine residues, and having a 3-hydroxydodec-5-enoyl group bonded, via an amide linkage, to the N-terminal leucine residue thereof. The peptides have an antiviral activity. A strain capable of producing the above peptides and belonging to a new species of genus Pseudomonas.