The anti-allergic effects of a 70% ethanol extract from Selaginella tamariscina herb (EST) were evaluated in this study. EST given at the doses of 500 and 1000mg/kg can inhibitmouse systemic anaphylactic shock induced by compound 48/80 in a dose-dependent manner.It can also dose-dependently block rat homologous passive cutaneous anaphylaxis and skinreactions caused by exogenous histamine and serotonin with a significant difference observedat the dose of 1000mg/kg. In addition, EST can reduce histamine release from rat peritonealmast cells triggered by compound 48/80 and an antigen in vitro. When incubated with ratmast cells, the extract (200μg/ml) can significantly elevate the intracellular cAMP levels.The finding suggests that EST inhibits mast cell-dependent, immediate allergic reactions. Itseffects appear to be mediated by reducing the release of vasoactive amines such as histaminefrom mast cells via stabilizing the cell membrane and weakening the inflammatory action ofthese amines. Based on these results, Selaginella tamariscina and one of its active componentsflavonoids may be useful as potential remedies for allergic rhinitis and other allergy-relateddiseases.