Mesenchymal stem cells (MSCs) have significant immunomodulatory effects in the development of acute lung inflammation and fibrosis. However, it is still unclear as to whether MSCs could attenuate allergic airway inflammation in a mouse model of asthma. We firstly investigated whether exogenous MSCs can relocate to lung tissues in asthmatic mice and analyzed the chemotactic mechanism. Then, we evaluated the in vivo immunomodulatory effect of exogenous MSCs in asthma. MSCs (2 × 10(6)) were administered through the tail vein to mice one day before the first airway challenge. Migration of MSCs was evaluated by flow cytometry. The immunomodulatory effect of MSCs was evaluated by cell counting in bronchoalveolar lavage fluid (BALF), histology, mast cell degranulation, airway hyperreactivity and cytokine profile in BALF. Exogenous MSCs can migrate to sites of inflammation in asthmatic mice through a stromal cell-derived factor-1α/CXCR4-dependent mechanism. MSCs can protect mice against a range of allergic airway inflammatory pathologies, including the infiltration of inflammatory cells, mast cell degranulation and airway hyperreactivity partly via shifting to a T-helper 1 (Th1) from a Th2 immune response to allergens. So, immunotherapy based on MSCs may be a feasible, efficient therapy for asthma.