Suplatast tosilate is an antiallergic drug that selectively suppresses Th2-cytokine production and inhibits airway hyperresponsiveness and eosinophilic airway inflammation. This drug has been also shown to improve pulmonary function and symptoms in steroid-dependent asthma, resulting in a decrease in doses of inhaled corticosteroid. However, the precise mechanism by which suplatast tosilate exerts an antiasthmatic effect in vivo remains to be known. Our previous study showed the polarization of circulating type 1 dendritic cells (DC1)/type 2 dendritic cells (DC2) balance toward DC2 in asthma, which might be associated with its Th2-dominant immune response. In the present study, we attempted to clarify the effect of suplatast tosilate on DC1/DC2 balance in asthma. Using multicolor flow cytometry, we enumerated circulating DC1 and DC2 before and 8 weeks after treatment with suplatast tosilate in nine patients with asthma. Before the treatment, the patients with asthma had a significant higher percentage of DC2 together with a significant lower ratio of DC1/DC2 compared with normal subjects. Administration of suplatast tosilate significantly decreased the percentage of DC2, but not that of DC1, resulting in a significant raises of the ratio of DC1/DC2. Concomitantly, intracellular cytokine analysis showed that the percentage of IL-4 producing CD4+ T cells was significantly decreased after the treatment. These data suggest that suplatast tosilate normalizes the polarized DC1/DC2 balance toward DC2 in asthma, which may also alter its Th2-dominant Th1/Th2 balance toward Th1.