As part of an ongoing search for plant-derived compounds that inhibit the activation of NF-kappaB, the methanol extract of the aerial parts of Isodon excisus was found to have significant inhibitory effects on the activation of NF-kappaB in murine macrophage RAW264.7 cells. Bioactivity-guided isolation of the extract yielded five new diterpenoids, excisusin A-E (1-5), along with seven known compounds, inflexarabdonin I (6), inflexarabdonin G (7), inflexin (8), inflexanin A (9), inflexanin B (10), inflexinol (11), and inflexarabdonin A (12). The structures were determined by analysis of the spectroscopic data including 2D NMR. All of the isolates were evaluated for their inhibitory effects on LPS-induced NF-kappaB activation and nitric oxide production in RAW264.7 cells.