A new verrucosane-type diterpenoid, bantamenside (1), along with six known compounds (2–7), was isolated from the Vietnamese liverwort Plagiochila bantamensis. The structure of the new compound was determined using comprehensive spectroscopic methods, including 1D and 2D NMR techniques as well as high-resolution mass spectrometry. Furthermore, all isolated compounds were evaluated for their ability to inhibit nitric oxide (NO) production. Compounds 1–3 and 6–7 demonstrated notable NO inhibitory activity, with IC₅₀ values ranging from 12.85 to 51.37 µM, outperforming or comparable to that of the positive control L-NMMA (IC₅₀ 41.30 ± 6.60 µM).