<jats:p>Two new butyrolactone I derivatives: 3‐[3‐hydroxy‐4‐(3‐methyl‐but‐2‐enyl)‐phenyl]‐5‐(−4‐hydroxybenzyl)‐4‐methyl‐dihydrofuran‐2(3H)‐one (1) and (Z)‐3‐[3‐hydroxy‐4‐(3‐methyl‐but‐2‐enyl)‐phenyl]‐5‐(−4‐hydroxybenzylidene)‐4‐methyl‐dihydrofuran‐2(3H)‐one (2), in addition to the previously described (S)‐methyl‐4‐hydroxy‐2‐[4‐hydroxy‐3‐(3‐methyl‐but‐2‐enyl)‐benzyl]‐3‐(4‐hydroxy‐phenyl)‐5‐oxo‐2,5‐dihydro‐furan‐2‐carboxylic acid methyl ester (3), were identified from a strain of <jats:italic>Aspergillus terreus</jats:italic> Thom (Trichocomaceae) isolated from desert soil. The antifungal activities of both intra‐ and extracellular metabolites of <jats:italic>A. terreus</jats:italic> grown on yeast extract sucrose and malt extract media were determined. Only the secondary metabolites of <jats:italic>A. terreus</jats:italic> grown on yeast extract sucrose medium were active against <jats:italic>Aspergillus fumigatus</jats:italic> RCMB 002008. The antifungal activity of <jats:italic>A. terreus</jats:italic> was attributed to the presence of the compounds (1) and (2), whose minimum inhibitory concentrations (MIC) against <jats:italic>A. fumigatus</jats:italic> were found to be 32.00 and 16.00 µg/mL respectively. Structure elucidation was carried out using UV spectrometry, electrospray ionization mass spectrometry (ESIMS), high resolution electron impact (HREIMS) spectrometry, <jats:sup>1</jats:sup>H‐ and <jats:sup>13</jats:sup> C‐NMR, proton–proton correlation spectroscopy (<jats:sup>1</jats:sup>H–<jats:sup>1</jats:sup>H Cosy), distortionless enhancement by polarization transfer (DEPT), heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlations (HMBC) spectroscopy. Copyright © 2012 John Wiley & Sons, Ltd.