Objectives : In this study, we investigated the effect of Cassia obtusifolia Linne (Cassiae Semen; CS) extract on ovalbumin (OVA)-induced allergic asthma in mice. Methods : CR was extracted with 70% ethanol. For in vitro study, HMC-1, human mast cells were treated with CS extract at 0.2 and <TEX>$0.5mg/m{\ell}$</TEX> for 1 h, and then stimulated with compound (C) 48/80 for 30 min. Primary spleenocytes were isolated from the spleen of mice, treated with CS extract for 1 h, and then stimulated with ConA for 24 h. For in vivo study, mice were sensitized at day 0, 7 and 14 with 0.2% OVA and then airway challenged using neublizer at day 21, 23, 25, and 27 to induced allergic asthma. CS extract at doses of 100 and 300 mg/kg body weight was orally administered during OVA challenge once per a day. The levels of allergic mediators such as histamine, OVA-specific IgE, IL-4, and <TEX>$IFN-{\gamma}$</TEX> were measured in the sera of mice or culture supernatants by EIA and ELISA, respectively. The expression of IL-4 and <TEX>$IFN-{\gamma}$</TEX> gene was determined by RT-PCR. The histopathological change of lung tissues was observed with hematoxylin and eosin (H&E) and Periodic acid Schiff (PAS) staining. Results : The treatment of CS extract in HMC-1 cells significantly inhibited C48/80-induced degranulation, and histamine release. The treatment of CS extract in spleenocytes suppressed the expression of IL-4 and <TEX>$IFN-{\gamma}$</TEX> mRNA. The administration of CS extract in OVA-induced asthmatic mice significantly decreased the levels of OVA-specific IgE, and IL-4 in a dose-dependent manner with OVA-control group. In addition, CS extract inhibited the infiltration of inflammatory cells and bronchiolar damage with epithelial thickening in lung tissues of OVA-induced asthma mice, and also mucin accumulation. Conclusions : These results indicate that CS extract prevents asthmatic damage through regulating the allergic immune response.