The structure of pillaromycinone (II) was elucidated. The ultraviolet (UV) spectrum of PMN tetraacetate (VI) was similar to that of 1, 2, 3, 4-tetrahydro-1-oxophenanthrene. On oxidative degradation pillaromycinone dimethyl ether (IX) gave 3-methoxy-1, 2, 4, 5-benzenetetracarboxylic acid (X) and 3-methoxyphthalic acid (XI). Zinc dust distillation of II gave anthracene and naphthacene. The UV spectrum of II resembles to that of anhydrodemethyltetracycline. From the chemical and spectrometric data the structure of β-substance (IV) was suggested to be 1, 2, 3, 4, 4a, 5, 12, 12a-octahydro-12-oxo-4, 10, 11, 12a-tetrahydroxynaphthacene. The nuclear magnetic resonance (NMR) and the spin decouplings of isopropylidene PMN (XVI) and PMN (II) gave the structure (3(S), 4(R), 4a(R), 12a(R)) 2-acetyl-3, 4, 4a, 5, 12, 12a-hexahydro-12-oxo-3, 4, 10, 11, 12a-pentahydroxynaphthacene to PMN (II).