Interleukin (IL)-33 is a recently described member of the IL-1 family and has been shown to induce production of T helper type 2 cytokines. In this study, an anti-IL-33 antibody was evaluated against pulmonary inflammation in mice sensitized and challenged with ovalbumin. The anti-IL-33 or a control antibody (150 microg/mouse) was given intraperitoneally as five doses before the sensitization and antigen challenge. Treatment with anti-IL-33 significantly reduced serum IgE secretion, the numbers of eosinophils and lymphocytes, and concentrations of IL-4, IL-5, and IL-13 in bronchoalveolar lavage fluid compared with administration of a control antibody. Histological examination of lung tissue demonstrated that anti-IL-33 significantly inhibited allergen-induced lung eosinophilic inflammation and mucus hypersecretion. Our data demonstrate for the first time that anti-IL-33 antibody can prevent the development of asthma in a mouse model and indicate that blockade of IL-33 may be a new therapeutic strategy for allergic asthma.