A new seven-membered lactone type meroterpenoid, isoterreulactone A, was isolated from the solid state fermentation of Aspergillus terreus and its structure was established by various spectral analysis. Isoterreulactone A inhibited acetylcholinesterase with an IC(50) value of 2.5 microM while did not inhibit butyrylcholinesterase even at 500 microM.