Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive form of lung disease characterized by fibrosis of the supporting framework (interstitium) of the lungs. By definition, the term is used only when the cause of the pulmonary fibrosis is unknown ("idiopathic"). Microscopically, lung tissue from patients shows a characteristic set of histologic/pathologic features known as usual interstitial pneumonia (UIP). UIP is therefore the pathologic counterpart of IPF.Idiopathic pulmonary fibrosis is characterized by radiographically evident interstitial infiltrates predominantly affecting the lung bases and by progressive dyspnea and worsening of pulmonary function. No therapy has been clearly shown to prolong survival. The current strict definition of idiopathic pulmonary fibrosis provides a new focus for basic and clinical research that will improve insight into the pathogenesis of this disorder and stimulate the development of novel therapies.

Pirfenidone has proven antifibrotic and anti-inflammatory properties in various in vitro systems and animal models of pulmonary fibrosis, although its precise mechanism of action remains unclear. It attenuates fibroblast proliferation, production of fibrosis-associated proteins and cytokines, and the increased biosynthesis and accumulation of extracellular matrix in response to cytokines such as transforming growth factor-β. It is also shown to slow tumor cell proliferation by inhibiting fibroblast growth factor, epidermal growth factor and platelet-derived growth factor.

Pirfenidone has not been widely approved for clinical use in China, in this study, safety and efficacy were evaluated to see if pirfenidone has a significant advantage over placebo in terms of improving lung function and life quality etc. (see primary and secondary criteria) or slows down the deterioration of lung function in Chinese subjects diagnosed with IPF.

Inclusion Criteria:

1. Written informed consent signed;
2. 18-75 years of age;
3. Clinically or multidisciplinarily diagnosed idiopathic pulmonary fibrosis(see 2011 guidance );
4. Resting state PaO2≥50mg, FVC%≥45% normal predicted value and DLCO≥30% normal predicted value.

Exclusion Criteria:

1. Allergic to pirfenidone;
2. Dyspnea symptoms relieved in the past 6 months;
3. Patients in acute exacerbation phase;
4. Diabetic patients whose fasting venous glucose >11.1 mmol/L;
5. Patients with malignant tumor and hemorrhagic diseases;
6. Patients with serious underlying pulmonary disease;
7. Patients with serious heart disease(NYHA class Ⅲ-Ⅳ), liver disease(ALT or AST 2 times above the upper level of normal value range), kidney disease(Cr above the upper level of normal value range);
8. Patients who has taken Acetylcysteine in the past 3 months;
9. Patients who has taken Prednisone>15mg/day(or other equivalent amount of glucocorticoid) and/or Immunosuppresants in the past 3 months;
10. Patients who has taken interferon, penicillamine, colchine or other agents for the treatment of IPF;
11. Pregnant or lactating women;
12. Participated in other clinical trials in the past 1 month;
13. The investigator assessed as inappropriate to participate in this clinical trial.