We studied the effect of Rosa davurica Pall. (Rosaceae) fruits (RdF) on immediate-type allergic reactions. RdF completely inhibited compound 48/80-induced systemic anaphylactic shock at the dose of 1 g/kg. When RdF was given as pretreatment, at concentrations ranging from 0.0001 to 1 g/kg, the serum histamine levels induced by compound 48/80 were reduced in a dose-dependent manner. RdF inhibited the passive cutaneous anaphylaxis activated by anti-dinitrophenyl (DNP) IgE antibody dose dependently. RdF also inhibited the histamine release induced by compound 48/80 or anti-DNP IgE from the rat peritoneal mast cells (RPMC). Moreover, RdF had a significant inhibitory effect on anti-DNP IgE-induced tumor necrosis factor-alpha production from RPMC. These results indicate that RdF may contain compounds with actions that inhibit mast cell degranulation in the rat.