Hosta plantaginea (Lam.) Aschers flower is traditionally used in China as an important herbal medicine for the treatment of inflammatory disease. The present study isolated one new compound, namely (3R)-dihydrobonducellin (1), and five known ones, p-hydroxycinnamic acid (2), paprazine (3), thymidine (4), bis(2-ethylhexyl) phthalate (5), and dibutyl phthalate (6) from H. plantaginea flowers. These structures were elucidated from spectroscopic data. Among them, compounds 1–4 remarkably suppressed nitric oxide (NO) production in lipopolysaccharide (LPS)-induced RAW 264.7 cells with half maximal inhibitory concentration (IC₅₀) values of 19.88 ± 1.81, 39.80 ± 0.85, 19.03 ± 2.35, and 34.63 ± 2.38 μM, respectively. Furthermore, compounds 1 and 3 (20 μM) significantly decreased levels of tumor necrosis factor α (TNF-α), prostaglandin E2 (PGE2), interleukin 1β (IL-1β), and IL-6. Additionally, compounds 1 and 3 (20 μM) prominently reduced the phosphorylation protein level of nuclear factor kappa-B (NF-κB) p65. The present findings indicated that compounds 1 and 3 may be new candidates against inflammation via blocking the NF-κB signaling pathway.