Mast cell-mediated anaphylactic reaction is involved in many allergic diseases such as asthma and allergic rhinitis. Phellinus linteus has been used as a traditional herb medicine in oriental countries and is known to have anti-tumor, immunomodulatory, anti-inflammatory, and anti-allergic activities. However, roles of Phellinus linteus in the mast cell-mediated anaphylactic reactions have not fully been examined. In the present study, we have investigated the effects of water extract from the fruiting body of Phellinus linteus (WEPL) on mast cell-mediated anaphylaxis-like reactions. Oral administration of WEPL inhibited the compound 48/80-induced systemic anaphylaxis-like reaction and ear swelling response. WEPL also inhibited the anti-dinitrophenyl (DNP) IgE-mediated passive systemic and cutaneous anaphylaxis. WEPL had no cytotoxicity on rat peritoneal mast cells (RPMC). WEPL dose-dependently reduced histamine release from RPMC activated by compound 48/80 or anti-DNP IgE. Moreover, WEPL decreased the compound 48/80-induced calcium uptake into RPMC. Furthermore, WEPL increased the level of intracellular cAMP and significantly inhibited the compound 48/80-induced cAMP reduction in RPMC. These results suggest that WEPL may serve as an effective therapeutic agent for allergic diseases.