Yin-Chiao-San (YCS), a kampo medicine, is widely used for patients with pulmonary disease and was applied for the treatment of SARS in Asia countries in 2003. For this reason, the present study investigated the preventive effect of YCS on bleomycin (BLM)-induced pulmonary fibrosis (PF) in rats. Animals were divided into four groups: (1) saline control group; (2) BLM-induced group, in which 15 mg/kg BLM was intraperitoneally injected three times per week for a period of 5 weeks; (3) BLM + vitamin E (10 mg/kg/day) as a positive group; (4) and BLM + YCS (1000 mg/kg/day). After 35 days, the rats were anesthetized, killed and then the lungs and bronchoalveolar lavage fluids (BALFs) were collected. The attenuation of pulmonary fibrosis was estimated according to the lung index, malondialdehyde (MDA), catalase (CAT), hydroxyproline (HP) and tumor necrosis factor-alpha (TNF-alpha) level in lung tissue and BALF. The serial sections of lung were stained with haematoxylin-eosin and Masson trichrome for histopathological observation of pulmonary fibrosis. The results indicated that YCS significantly reduced the lung index, MDA, HP and TNF-alpha, but YCS significantly enhanced the CAT level when compared with the BLM-induced group (p < 0.05). Additionally, the BLM group displayed severe histopathological change in the lung tissue, but YCS treatment could attenuate the BLM-induced PF. In conclusion, the results demonstrated that YCS possesses antioxidant and antiinflammatory activities and also inhibited collagen formation. Thus, YCS exhibited a preventive effect in BLM-induced PF and it is suggested that YCS may be applied to attenuate the side effects of BLM in chemotherapy.