Chronic inflammation, which results from continuous exposure to antigens, is one of major reasons for tissue damage and diseases such as rheumatoid arthritis and type 2 diabetes. In this study, we investigated the anti-inflammatory effects of extracts (hexane, CHCl3, MeOH, MeOH/H2O, and H2O) from GW10-45, which is our new cultivar of an edible mushroom Pleurotus ferulae (ASI 2803 and ASI 2778), in RAW264.7 murine macrophages. None of the extracts showed cytotoxicity in RAW264.7 cells and the hexane, CHCl and H extracts reduced nitric oxide (NO) production, an important inflammatory marker, in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. Particularly, the extract (CG45) inhibited NO production more than the other extracts did. To elucidate the effects of CG45 on molecular targets involved in proinflammatory responses, we performed western blot analysis. Expression of inducible nitric oxide (iNOS) significantly decreased in LPS and CG45 co-incubated cells compared to that in LPS only-treated cells. Additionally, another protein thatplays a critical role in inflammation, was down-regulated in cells treated with both LPS and CG45. In the nuclear factor (NF)- B pathway, phosphorylation of I Bα decreased in RAW264.7 cells treated with both LPS and CG45. Furthermore, CG45 inhibited the phosphorylation of NF- B in LPS-stimulated RAW264.7 cells. Conclusively, CG45 could suppress proinflammatory responses in LPS-stimulated RAW264.7 cells by down-regulating not only the phosphorylation of NF- B and I Bα but also the expression of iNOS and COX-2 without any cytotoxicity.