Background: Pinoresinol, an ingredient in Gnetum montanum Markgr, has been demonstrated to be an anti-inflammatory substance. However, the anti-inflammatory activity of pinoresinol requires further research. Objectives: This study elucidates the effects of pinoresinol from Vietnamese G. montanum Markgr in suppressing lipopolysaccharide (LPS)-stimulated inflammation and the production of reactive oxygen species (ROS) in macrophages. Methods: Methanol was used to extract pinoresinol from Vietnamese G. montanum Markgr. The purity of pinoresinol was evaluated by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). Cytokines were measured by enzyme-linked immunosorbent assay (ELISA). The phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and p38 was analyzed by Western blot assay. Immunofluorescence was used to measure ROS generated from Raw 264.7 cells. Results: Lipopolysaccharide-mediated secretion of proinflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-1β was significantly decreased by pinoresinol (40 µg/mL, P < 0.001). Furthermore, LPS-induced phosphorylation of ERK1/2 and p38 was markedly suppressed by pinoresinol (40 µg/mL, P < 0.001). Importantly, ROS generated by LPS in macrophages was inhibited by pinoresinol at a concentration of 40 µg/mL (P < 0.001). Conclusions: These data further elucidate the anti-inflammatory pathways of pinoresinol, targeting the mitogen-activated protein kinase (MAPK) signaling pathways and ROS.