New acylpeptide antibiotics named cepafungins I, II and III were isolated from the culture broth of a strain identified as Pseudomonas sp. These antibiotics are neutral substances, soluble in aqueous alcohols and dimethyl sulfoxide, and show UV maxima at 260.5 nm. The IR spectra indicated these to be peptides. Molecular formulas C28H46N4O6, C27H44N4O6 and C26H42N4O6 for cepafungins I, II and III were indicated by elemental analysis and SI-MS. In the course of our screening work for new antibiotics from bacterial strains, a strain designated CB-3 and identified as Pseudomonas sp. was found to produce antibiotics active against fungi and murine leukemia P388. The antibiotics named cepafungins I, II and III were isolated and determined to be acylpeptides having an interesting 12-membered ring. The structures are presented in the following paper1). In this paper, the taxonomy of the producing strain, the isolation, physico-chemical properties as well as the biological activities are presented.