To investigate the suitability of the green alga Cladophora wrightiana, grown in the southern regions of the Korean Peninsula, as a source of anti-inflammatory agents for human use. Anti-inflammatory effects of the ethyl acetate extracts of C. wrightiana (CWE) were evaluated on lipopolysaccharide (LPS)-treated RAW 264.7 macrophages. CWE were examined for their ability to inhibit pro-inflammatory mediators and cytokines, such as nitric oxide (NO), prostaglandin E2 (PGE2), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β. To elucidate its inflammatory mechanisms, CWE was investigated as an inhibitor of mitogen-activated protein kinase (MAPK) in LPS-stimulated RAW 264.7 cells. Our results demonstrate that CWE potently inhibited LPS-induced NO production, with IC50 values of 61.25 µg/mL. Consistent with these findings, CWE reduced the LPS-induced expression of inducible NO synthase (iNOS) protein in a concentration-dependent manner, as determined using western blot analysis. Furthermore, the levels of PGE2, TNF-α, IL-6, and IL-1β released into media were reduced by CWE in a concentration-dependent manner. In addition, CWE also induced a dose-dependent inhibition of the phosphorylation of mitogen activated protein kinases (MAPKs, JNK, and ERK). Collectively, the results of this study demonstrate that CWE reduces the levels of pro-inflammatory mediators and cytokines including NO, PGE2, IL-1β, TNF-α, and IL-6 via suppression of JNK and ERK phosphorylation in RAW 264.7 cells. These findings reveal, in part, the molecular basis underlying the anti-inflammatory properties of CWE.