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Marine-derived fungi are considered to be valuable producers of bioactive secondary metabolites used as lead compounds with medicinal importance. In this study, chemical investigation of the seawater-derived fungus Aspergillus sydowii SW9 led to the isolation and identification of one new quinazolinone alkaloid, 2-(4-hydroxybenzyl)-4-(3-acetyl)quinazolin-one ( 1 ), one new aromatic bisabolene-type sesquiterpenoid, ( 2 ) and one new chorismic acid analogue ( 3 ), as well as two known alkaloids (compounds 4 and 5 ). Their structures were determined by extensive 1D/2D NMR and mass spectrometric data, and the absolute configurations of 2 and 3 were assigned by the analysis of ECD spectra aided by quantum chemical computations. Compounds 1 , 2, and 4 exhibited selective inhibitory activities against the human pathogenic bacteria Escherichia coli , Staphylococcus aureus , S. epidermidis, and Streptococcus pneumoniae , with MIC values ranging from 2.0 to 16 μg/mL.