Structures of new antibiotics SF2415A1, A2, A3, B1, B2 and B3 were deduced from spectroscopic analyses and degradation studies. The structure of SF2415A3, which has the most antibacterial activity, was proposed to be 3,4a-dichloro-9-diazo-3,4, 4a,10a-tetrahydro-6-hydroxy-2,2,7-trimethyl-10a-[(E)-3,7-dimethyl- 2,6-octadienyl]-(2H,9H)naphtho-[2,3-b]pyran-5,8,10-trione. All of antibiotics SF2415 have a semi-naphthoquinone structure.