Theissenia cinerea 89091602 is a previously reported plant-derived bioactive fungal strain, and the active principles separated from the extracts of its submerged culture were shown to exhibit potent anti-neuroinflammatory activities in both cellular study and animal testing. In a continuation of our previous investigation on the bioactive entities from this fungus, solid state fermentation was performed in an attempt to diversify the bioactive secondary metabolites. In the present study, five previously unreported polyketides, theissenophenol (1), theissenepoxide (2), theissenolactone D (3), theissenone (4), and theissenisochromanone (5), together with the known theissenolactone B (6), theissenolactone C (7), and arthrinone (8), were isolated and characterized through spectroscopic analysis and comparison with the literature data. The configurations of theissenepoxide (2) and theissenisochromanone (5) were further corroborated by single-crystal X-ray diffraction data analysis. Theissenone (4), theissenolactone B (6), theissenolactone C (7), and arthrinone (8) exhibited potent nitric oxide production inhibitory activities in murine brain microglial BV-2 cells with IC50 values of 5.0 ± 1.0, 4.5 ± 0.6, 1.1 ± 0.1, and 3.2 ± 0.3 μM, respectively, without any significant cytotoxic effects.