A new ubiquitin-activating enzyme (E1) inhibitor, himeic acid A, was isolated from a culture of marine-derived fungus, Aspergillus sp. The structure was determined by spectroscopic analysis. The formation of an E1-ubiquitin (Ub) intermediate was 65% inhibited by himeic acid A at the concentration of 50 microM, while two new related compounds, himeic acids B and C, showed little inhibitory activity even at 100 microM.