Four new bisanthraquinones, dothideomins A-D (<b>1</b>-<b>4</b>), were identified from <i>Dothideomycetes</i> sp. BMC-101, an endophytic fungus isolated from <i>Magnolia grandiflor</i>a L. leaves. Their chemical structures were established by NMR analysis, single-crystal X-ray crystallography, and ECD analysis. Dothideomins A-D (<b>1</b>-<b>4</b>) were characterized by an unusual 6/6/6/5/6/3/6/6 octocyclic scaffold (<b>1</b> and <b>2</b>) and a 6/6/6/5/6/6/6 heptacyclic scaffold (<b>3</b> and <b>4</b>), respectively. All compounds, especially <b>1</b> and <b>3</b>, exhibited potent antibacterial activity with MIC values ranging from 0.4 to 0.8 μg/mL.