Abstract: A substance having antibiotic activity, designated as cytophagin, which is stable in the form of colorless powder and which has an elemental analysis of H: 6.94%, C: 47.22% and N: 13.21%, a molecular weight of 1,000 to 1500. This substance is believed to be composed of 11 amino acids and exhibits a strong activity against Gram-positive bacteria. Cytophagin is produced by fermentation using a microorganism belonging to the genus Cytophaga and capable of producing cytophagin. A preferred strain is Cytophaga BMF 694-N3 (FERM P-4846;NRRL B-12109). Cytophagin is of potential interest as medicament or veterinary agent because of its antibiotic activity.