The present invention relates to a pharmaceutical composition for preventing or treating asthma, the composition containing styraxlignolide A or an aglycone thereof as an active ingredient. More particularly, styraxlignolide A compound is one separated from stems and barks of Styrax japonica, and styraxlignolide A or homoegonol, which is an aglycone of styraxlignolide A and which has improved safety, has the effect of attenuating weight loss and airway hyperresponsiveness, inhibiting the generation of reactive oxygen species in airway, inhibiting generation of IgE, TGF-²1, and IL-17 in the serum and bronchoalveolar lavage fluid, inhibiting endobronchial inflammatory cell infiltration, and inhibiting the formation of a mucous plug and subepithelial fibrosis in an asthma-induced mouse model. Therefore, 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.