Abstract: Objective: To observe the effect of Th1 /Th2 type cytokines in pulmonary fibrosis pathogenesis. Methods: Forty male Kunming mice were randomly divided into 3 groups，8 mice in control group were intratracheal injection with saline， and executed on the 7th day; 16 mice in model group were intratracheal injection with bleomycin. Sixteen mice in treatment group were intraperitoneal injection with interferon- and captopril by oral gavage on the day after model-building，4 mice were executed once on the 3rd，7th， 14th and 28th day. Bronchus alveolus lavage fluid( BALF) was collected， the levels of interleukin( IL-4) and IL-12 in BALF were detected by ELISA method. The right lung specimen was collected in control and model groups，and pathological semi-quantitative analysis of alveolitis degree was detected. Results: Compared with control group， IL-12 level in BALF in model group was reduced( P ＜ 0. 01) ; IL-4 level was increased( P ＜ 0. 01) ，Th2 dominant expression was expressed. Compared with model group， IL-12 level in BALF in treatment group was increased( P ＜ 0. 01) ; IL-4 level was reduced( P ＜ 0. 01) ，partly recovered to the dynamic balance of Th1 /Th2. Compared with model group， there was no difference on alveolus inflammation in treatment group at early stage ( 3rd，7th day) ， the degree of alveolus inflammation fibrosis was reduced obviously at later stage( 28th day ) ( P ＜ 0. 01) . Conclusions: Th1 /Th2 cytokine balance disorder is one of mechanism of bleomycin-leading pulmonary fibrosis; combined with interferon- and captopril may partly restore Th1 /Th2 cytokine balance， and lighten the alveolitis ＆ pulmonary fibrosis at the later stage.