Objectives : The aims of this study were to exploring the therapeutic effect of Imperatae Rhizoma Extract(IRE) on Asthma. Methods : To investigate biological modulation activities of IRE, we conducted the cell-based assay whether IRE could regulate T helper 2 cells activity with EL4 T cells and mouse splenocytes, and followed animal study to conform the efficacy of their therapeutic potential on OVA-induced asthmatic mouse. Results : In cell study, IRE suppress the nuclear translocation of GATA binding protein-3 protein in phorbol 12-myristate 13-acetate/Ionomycin-stimulated EL4 T cells and Interleukine(IL)-4, IL-5 and IL-13 production in splenocytes at concentration dependent manner. In animal study, IRE-treated groups both 100mg/ml and 200mg/ml improve airway hypersensitibility reaction(AHR) response to methacholine about 30% and 40% with positive control group. Peritoneal blood analysis reveal that eosinophil number and ovalbumin-specific IgE is reduced by IRE treatment. Cell number of eosinophil is also reduced in bronchoalveolar lavage of IRE group like to peritoneal cell and real time-polymerase chain reaction data show that expression levels of IL-4, IL-5 and IL-13 were down regulated in lung tissue. Finally, histological analysis indicate that IRE protect the bronchial tissue damages through the accumulation of inflammatory cells and collagen, and these effect may be cause by interfering Th2 cells activity. Conclusions : Our data represent that IRE potentiates therapeutic activities to the allergic diseases such as asthma by regulating Th2 cells differentiation.