Background and Purpose: Asthma is a chronic inflammatory lung disorder with continuously increasing prevalence worldwide. Novel strategies are needed to prevent or improve asthma. The aim of this study was to investigate the effects of sophoricoside from Sophora japonica on allergic asthma. Experimental Approach: Sophoricoside was isolated from the mature seeds of S. japonica. Allergic asthma and passive cutaneous anaphylaxis (PCA) models were generated by ovalbumin (OVA) treatment or antibody-allergen reaction in mice. Allergic and asthmatic symptoms, immune cell infiltration, and the amounts of histamine, lipid metabolites, and pro-inflammatory cytokines were determined, and in vitro CD4+ T cell differentiation was performed. Key Results: The mature seeds of S. japonica contain a large amount of sophoricoside. Sophoricoside reduced allergic and asthmatic symptoms by suppressing airway inflammation and antibody-antigen reaction in mouse models. In particular, sophoricoside suppressed immune cell recruitment into the airway lumens of the lungs and production of pro-inflammatory cytokines in the bronchoalveolar lavage fluid (BALF) of OVA-induced mice. It also decreased the amounts of histamine and lipid metabolites released in OVA-induced mice and antibody-antigen stimulated mast cells. In addition, sophoricoside decreased differentiation of naïve CD4+ T cells into T helper type 1 (Th1), Th2, and Th17 cells. Conclusions and Implications: Sophoricoside from S. japonica inhibited allergic asthma by suppressing mast cell activation and CD4+ T cell differentiation. Thus, it is a promising candidate molecule for the treatment of allergic asthma. Keywords Airway inflammation; Allergic asthma; CD4+ T cell; Mast cell; Ovalbumin; Sophora japonica; Sophoricoside