This study investigated the inhibitory effect of a glycoprotein isolated from Cudrania tricuspidata Bureau (CTB glycoprotein) on di(2-ethylhexyl) phthalate (DEHP)-induced mast cell degranulation and related signaling cascade in RBL-2H3 cells. This experiment evaluated the intracellular Ca2+ level, and the activities of protein kinase C (PKC), mitogen-activated protein kinase (MAPK), transcription factor, and the cytokines in DEHP-treated RBL-2H3 cells. Our results revealed that the CTB glycoprotein in the presence of DEHP inhibits the release of histamine and expression of interleukin (IL)-4, IL-6, and TNF-α in RBL-2H3 cells. We also found that the CTB glycoprotein inhibits the intracellular Ca2+ level, translocation of PKC from cytosol to membrane and the phosphorylation of ERK1/2 in cells. Moreover, the CTB glycoprotein (100 µg/ml) has suppressive effects on transcriptional activation of nuclear factor (NF)-κB in DEHP-treated RBL-2H3 cells. The activation of NF-κB was collectively blocked by treatment with PKC inhibitor (staurosporine) as well as ERK1/2 inhibitor (PD98059), respectively. The results from these experiments indicated that the CTB glycoprotein inhibits release of histamine and expressions of IL-4, IL-6, and TNF-α via down regulations of PKC/MAPK and NF-κB on the stage of mast cell degranulation induced by DEHP. Moreover, oral administration of CTB glycoprotein (10–20 mg/kg) inhibited compound 48/80-mediated systemic reaction in mice. In conclusion, we speculated that the CTB glycoprotein might be one component for preparation of health supplements for prevention of allergic immune disorders. J. Cell. Biochem. 109: 124–131, 2010. © 2009 Wiley-Liss, Inc.