The tuberous roots of Liriope platyphylla (Liriopis Tuber; LT) is traditionally used in Korean Medicine for treating colds, cough, and sputum production. In this study, we investigated the effect of spicatoside A isolated from LT methanol extract on ovalbumin (OVA)-sensitized/challenged asthmatic mice. For induction of allergic asthma, BALB/c mice were sensitized with OVA by an intraperitoneal injection at three times a week, and then challenged into the nasal cavities using a nebulizer. Spicatoside A at dose of 1mg/kg body weight was treated in mice with an oral administration once daily for a week during OVA challenge. The concentrations of OVA-specific IgE, IL-4, IL-5 and IL-13 were measured in the sera or bronchoalveolar lavage fluids (BALF) of mice by enzyme-linked immunosorbent assay (ELISA). The numbers of total cells, macrophages, lymphocytes, neutrophils and eosinophils were counted in BALFs using Diff-Quik staining, and histopathological changes of lung tissues were observed by hematoxylin and eosin (H&E), Periodic acid Schiff (PAS) and Masson's trichrome staining. The purity of spicatoside A was 98.1% with a white powder (yield: 465.6mg). The treatment of spicatoside A in asthmatic mice significantly decreased the production of allergic mediator, OVA-specific IgE and Th2 cytokines, IL-4, IL-5 and IL-13 in sera and BALF. The numbers of inflammatory cells such as macrophages, lymphocytes, neutrophils and eosinophils in BALF of asthmatic mice were significantly reduced by the treatment of spicatoside A. Furthermore, the treatment of spicatoside A in asthmatic mice inhibited the structural damages of lung tissues with thickened bronchiolar epithelium and infiltration of inflammatory cells, the accumulation of mucus by the goblet cells hyperplasia and collagen in the bronchioles. These results suggest that spicatoside A of LT has a preventive effect on allergic asthma through the inhibition of lung inflammation and allergic response.