Dehydroepiandrosterone, an androgen abundant in circulation, has important immunomodulating effects. In this study the therapeutic effect of dehydroepiandrosterone on established allergic inflammation was examined in a dust mite (Dermatophagoides farinae)-induced asthma model. Airway inflammation was provoked in D. farinae-sensitized BALB/c mice by repetitive intratracheal challenge (3 times, once a week). Three days after the first challenge, mice were fed a diet incorporated with 1.5% (w/w) dehydroepiandrosterone and were examined at days 3 and 6 after the last challenge. Airway challenge resulted in pulmonary eosinophilic inflammation accompanied by elevated blood eosinophil counts and elevated serum and bronchoalveolar lavage immunoglobulin E antibody levels in control diet-fed mice. However, the D. farinae-induced airway inflammation and blood eosinophilia was significantly reduced in dehydroepiandrosterone-fed mice, which was associated with a decrease in serum interleukin-4, interleukin-5, and interferon-gamma levels. Total immunoglobulin E antibody concentrations in serum and bronchoalveolar lavage fluids were not affected by the dehydroepiandrosterone treatment. These results demonstrated that dehydroepiandrosterone could suppress preexisting allergic airway inflammation.