Traditional Chinese medicine has a long history of application in the treatment of bronchial asthma. Solid scientific evidence, however, is not available despite its widespread use among patients worldwide and in Taiwan. To assess the effect of Ding Chuan Tang (DCT) in airway hyper-responsiveness (AHR) on asthmatic children via randomized, double blind, placebo-controlled clinical trial. This study enrolled children who were aged 8-15 and diagnosed as mild to moderate persistent asthma patients. They were randomly allocated to receive 6.0 g DCT or placebo daily for 12 wk. Self-recorded daily symptom scores, medication scores, and morning and evening peak expiratory flow rates were returned at the monthly clinic. Pulmonary function test, methacholine challenge test, and serum inflammatory mediators were measured before and at the end of the trial. Fifty-two asthmatic children completed the clinical study. Twenty-eight patients were assigned to the treatment group and 24 to the placebo group. At the end of the treatment period, AHR determined by log PC(20) was significantly improved in the DCT group (0.51 +/- 1.05 mg/ml vs. 0.26 +/- 0.84 mg/ml, p = 0.034). The total clinical and medication reduced parameters showed improvement in the DCT group (p = 0.004). The AHR, symptom and medication scores in children with persistent asthma were significantly improved with DCT treat for 12 wk. The results suggested more stable airways achieved with such an add-on complementary therapy.