The effective microorganism fermentation extract (EM-X) is an antioxidant cocktail derived from the fermentation of plant material with effective microorganisms, and its clinical application is being increasingly scrutinized. In the current study, the antiasthmatic effect of EM-X was investigated using a mouse model. Inhalation of EM-X during OVA challenge resulted in a significant reduction in airway hyperreactivity (AHR) and airway recruitment of leukocytes including eosinophils. However, the level of 8-isoprostane in bronchoalveolar lavage fluid (BALF), a marker of oxidative stress in asthmatic patients, was unaltered by EM-X inhalation. Instead, ELISA data showed that levels of IL-4, IL-5 and IL-13 in BALF or lung tissues were significantly lower in EM-X-inhaling mice than in the control mice, but not the IFN-gamma level. A considerably lower amount of Ag-specific IgE and IgG1 was detected in the serum of EM-X-inhaling mice than in the serum of the controls, whereas their IgG2a secretion was similar. In addition, Ag-specific ex vivo IL-4, IL-5 and IL-13 production of draining lymph node cells was markedly diminished by EM-X inhalation, but not IFN-gamma. These data clearly show that inhaled EM-X suppresses type 2 helper T (TH2), but not type 1 helper T (TH1), response. In conclusion, inhalation of EM-X attenuates AHR and airway inflammation which results from selective inhibition of the TH2 response to allergen, but independently of antioxidant activity. Our data also suggest that EM-X may be effectively applied for control of allergic asthma.