Asthma is a chronic lung disease characterized by allergen-induced airway inflammation and orchestrated by Th2 cells. Interleukin-12, a Th1-promoting cytokine, is capable of inhibit the Th2-driven allergen-induced airway changes and therefore considered as an attractive molecule to treat asthma. Recent epidemiological and clinical studies suggest a possible role of Lactococcus lactis in the prevention of allergic diseases. In this study, we evaluated the immunomodulatory effects of live L. lactis secreting a biologically active form of IL-12 (LL-IL12) in a mouse model of ovalbumin (OVA)-induced asthma. Intranasal mice administration with LL-IL12 resulted in a shift Th2 to Th1 with elevated IFN-gamma and decreased IL-4 levels. In addition, a profound decrease in airway hyper-responsiveness and pulmonary inflammation was also observed in mice administered with LL-IL12. These promising preclinical results suggest the feasibility of this approach to be used in the treatment of asthma.