Allergic asthma is a chronic inflammatory disorder of airways, which is characterized by attacks provoked by exposure to so-called asthma triggers, such as pet dander, second-hand tobacco smoke, dust mites, and mold spores. B7-1 (CD80), perhaps one of the most studied co-stimulatory molecules involved in asthma, plays a key role in regulating allergen-induced T cell activation in asthma, probably through T cell recruitment and Th cell differentiation upon allergen provocation. The present study was designed to test the hypothesis that anti-B7-1 antibody has therapeutic effects in asthma by blocking B7-1/CD28 pathway. The asthma model was established by ovalbumin (OVA) sensitization and challenging in female Balb/c mice. One hour after the last induction, mice were sacrificed and whole lung lavage was conducted. Cell numbers in bronchoalveolar lavage fluid (BALF) were determined and the expression levels of IFN-gamma and IL-4 in supernatant were measured by an enzyme-linked immunosorbent assay method. Sedimental cells smears were stained with Wright's-Gimsa mixed coloring method. The B7-1 expression was detected by immunohistochemistry method with frozen tissue sections. The anti-B7-1 antibody treatment could alleviate asthmatic syndromes induced by OVA. The number of recoverable eosinophils in BALF in the anti-B7-1 antibody treated group was significantly lower than that in the control group (P<0.01) and the eosinophils peribronchial infiltration was remarkably reduced in anti-B7-1 treated asthmatic mice, based on histological evaluation. The treatment with the anti-B7-1 antibody induced IFN-gamma expression and decreased IL-4 expression, compared with the asthmatic control group (P<0.01). In conclusion, the anti-B7-1 antibody approach may provide a novel therapy for allergic asthma.