The currently accepted approaches to treatment of pulmonary fibrosis are based on the treatment of alveolitis and pulmonary fibrosis, however clinically available anti-inflammatory and antifibrotic agents are not often beneficial. Hu-qi-yin, one of the traditional Chinese herbal formulas, has been used for clinical therapy of pulmonary fibrosis in China. The aim of the present study is to evaluate the preventive effects of Hu-qi-yin on the bleomycin (BLM)-induced pulmonary fibrosis in rats. The degree of fibrosis was evaluated with hydroxyproline contents in serum and lung tissue 28 days post-BLM instillation. The semi-quantitative analyses of lung sections were conducted to evaluate the intensity of alveolitis and fibrosis. Furthermore, the expression of transforming growth factor-beta(1) (TGF-beta(1)) was quantitatively studied at the protein and mRNA levels by immunohistochemistry and in situ hybridization, respectively. Oral treatment with Hu-qi-yin improved the body weight loss of rats in doses of 3.8, 7.6g/kg compared with BLM-treated control group, and significantly inhibited the alveolitis and pulmonary fibrosis in a dose-dependent manner as reflected by decreases of the hydroxyproline contents of serum and lung, and amelioration of alveolitis and pulmonary fibrosis fraction 28 days after BLM administration. The one of the possible mechanisms of the protective effect of Hu-qi-yin was via reduction of the overexpression of TGF-beta(1) protein and mRNA. These results suggested a great potential that Hu-qi-yin might be effective in the treatment of pulmonary fibrosis.