Ophiosphaerellins A-I (1-9), the first example of bicyclo[4.1.0]heptenones, as well as their biosynthetic relatives ophiosphaerekorrins A-B (10-11) were isolated from the endolichenic fungus Ophiosphaerella korrae. Biosynthetically, they were derived from the polyketide pathway, and their absolute configurations were determined on the basis of the combination analysis of spectral data, circular dichroism calculations, and single-crystal X-ray diffraction measurement. Preliminary test with thin-layer chromatography bioautography found that this type of compounds showed moderate acetylcholinesterase (AChE) inhibitory effects.