Paulomycin was originally isolated as a mixture of antibiotics now designated paulomycins A and B, which have excellent antibacterial activity against organisms resistant to other antibiotics. The present communication reports the structures of paulomycins A and B (1a and 1b), members of a family of antibiotics with hitherto unreported structures, and the evidence for these structures. Studies included conversion of 1a to paulomycinone A (2) and paulomenol A (5), acidic methanolysis to form 11-O-pauloylpaulinone (7) and methyl 7-O-(2-methylbutyryl)paulomycoside (8), periodate oxidation of methyl paulomycoside (9), and analysis of spectral data (¹H NMR, ¹³C NMR, mass spectrum) and chemical properties. These data strongly favor structures 1a and 1b for paulomycins A and B.