Allergic asthma is an inflammatory airway disease caused by T helper type 2 (Th2)-driven immune responses. Recent studies have demonstrated that adipose-derived stromal cells (ASC) have an immunosuppressive effect on T-cell activity. This study was performed to investigate whether ASC can inhibit Th2-dependent allergic airway inflammation in mice. BALB/c mice were sensitized to ovalbumin (OVA) by intraperitoneal injection. To investigate the effect of ASC on the development of asthma phenotypes, 2 × 10⁶ ASC were injected intravenously before OVA challenge. We evaluated the airway hyperresponsiveness (AHR), the proportion of eosinophils and cytokine production in bronchoalveolar lavage fluid (BALF), airway inflammation, and the intracellular cytokine staining of T cells in the BALF and spleen. Airway hyperresponsiveness, airway eosinophilia, and mucus production were markedly reduced after ASC administration before OVA challenge. The increased interleukin (IL)-4, IL-5, and transforming growth factor (TGF)-β1 levels in the BALF after OVA challenge were significantly reduced by the administration of ASC. This inhibition was accompanied by decreased IL-4(+) CD4(+) T cells and increased interferon (IFN)-γ(+) CD4(+) T cells in the BALF and spleen. The results of this study suggest that ASC administration before an allergen challenge inhibits AHR, lung inflammation, and Th2 cytokine production induced by an allergen challenge through inhibition of Th2 cell activity.