Objective To assess the value of serum amyloid A(SAA)in patients with acute exacerbation of chronic pulmonary diseases. Methods Seventy AECOPD patients were randomly chosen. The AECOPD patients were divided into bacterial infection induced group and non-bacterial infection induced group by sputum bacteria culture. Thirty five SCOPD patients were chosen as control group. General data was collected. Lung function ,chest X ray,blood routine,CRP,SAA,IL6 and PCT were deteced and compared in the 3 groups. The diagnostic value of SAA to distinguish bacterial infection induced AECOPD was estimated. Results SAA of both AECOPD sub-groups were significantly higher than that of healthy controls. SAA in infection group is higher that that in exacerba-tion group. In terms of ROC curve,AUC was 0.8682 for SAA to distinguish merging bacterial infection,and the cut-off value was 72.10 mg/L with sensitivity of 94.29% and specificity of 65.71%. Conclusion SAA increases in AECOPD patients,and more obviously in AECOPD patients with bacterial infection. SAA may be used as a reliable biomarker not only to distinguish AECOPD patients from SCOPD patients ,but also distinguish merging bacterial infection during AECOPD.