The present invention relates to a pharmaceutical composition containing styraxlignolide A or the aglycone thereof as an active ingredient for preventing or treating asthma. More particularly, the styraxlignolide A compound is separated from the stem and bark of Styrax japonica, and the styraxlignolide A or homoegonol, which is the aglycone of styraxlignolide A and which has improved safety, has the effect of attenuating weight loss and hypersensitivity of the airway, inhibiting the generation of active oxygen in the airway, inhibiting the generation of IgE, TGF-beta 1, and IL-17 in the serum and bronchoalveolar lavage fluid, inhibiting inflammatory cell infiltration in the bronchial tubes, and inhibiting the formation of a mucous plug and subepithelial fibrosis in an asthmatic mouse model. Therefore, the above-described styraxlignolide or homoegonol can be effectively used as the active ingredient of a pharmaceutical composition for preventing or treating bronchial asthma in which airway remodeling has progressed.