V-domain immunoglobulin suppressor of T-cell activation (VISTA) is a novel immune checkpoint receptor and ligand that regulates T-cell activation. We investigated the functional involvement of VISTA in T_h2 cell-mediated immune responses using an ovalbumin (OVA)-induced allergic asthma model. Treatment with an anti-VISTA monoclonal antibody (mAb) during allergen sensitization increased the production of antibodies, including total IgE, OVA-specific IgG1 and IgG2a and allergen-specific IL-5 and IL-13; it also increased the expression of IL-13 by splenic CD4⁺ T cells. However, treatment with the anti-VISTA mAb during sensitization did not accelerate asthmatic responses, including airway hyper-responsiveness (AHR) or the number of eosinophils in bronchoalveolar lavage (BAL) fluid. In contrast, treatment with the anti-VISTA mAb during allergen challenge significantly augmented AHR and BAL fluid eosinophilia. This treatment also increased the production of IL-5 and IL-13 in BAL fluid and the expression of IL-13 by CD4⁺ T cells in draining lymph nodes. These results suggest that VISTA is involved in the regulation of T_h2 cell generation and T_h2 cell-mediated antibody production and regulates asthmatic responses, especially in the effector phase.