We report the unambiguous assignments of the 1H and 13C NMR spectra of one new natural product, namely, 6,8‐di‐O‐methyl versiconol (1) together with one known anthraquinone aversin (2) and two xanthones 5‐methoxysterigmatocystin (3) and sterigmatocystin (4). These compounds were all isolated from the mangrove endophytic fungus ZSUH‐36 from the South China Sea. 1D and 2D NMR experiments including COSY, HMQC and HMBC were used to elucidate the structures. Variations in the 1H NMR spectrum of 6,8‐di‐O‐methyl versiconol (1) were also observed in the temperature range 25–75 °C. In addition, the plausible biogenetic path from 1 to 2 is discussed. Copyright © 2007 John Wiley & Sons, Ltd.