Mushrooms have become an important source of natural antitumor, antiviral, antibacterial, immunomodulatory, and anti-inflammatory agents. Golden oyster mushroom, Pleurotus citrinopileatus , is a common mushroom in oriental countries for human consumption. The present study investigated the anti-inflammatory reaction of the bioactive nonlectin glycoprotein (PCP-3A) isolated from the fresh fruiting body of this mushroom. Western blot analysis on LPS-induced iNOS, COX-2, and NF-κB expressions in RAW 264.7 cells as affected by PCP3-A was performed to elucidate the mechanism of NO and PGE2 reduction. The results showed that PCP-3A failed to affect RAW 264.7 viability at a concentration up to 6.25 μg/mL, but inhibited LPS (1 μg/mL)-induced expression, and that PCP-3A inhibited the production of NO and PGE2 in LPS-activated macrophages via the down-regulation of certain pro-inflammatory mediators, including iNOS and NF-κB.