Abstract： Objective To explore the relationship of inflammatory response of the respiratory tract and prognosis of chronic obstructive pulmonary diseases (COPD) patients undergoing mechanical ventilation (MV) in respiratory intensive care unit (RICU). Methods Thirty patients with COPD undergoing MV were involved in the study, and divided into survival group (n=16) and non-survival group (n=14). Exhaled breath condensate (EBC) was collected on day 1,3,5,7 after MV. The concentration of hydrogen peroxide (H2O2) in EBC was measured fluorimetrically. The content of interleukin-6(IL-6) in EBC was measured by enzyme-linked immunosorbent assay (ELISA). Results ①The significantly lower H2O2 and IL-6 levels in the survival group were observed on days 3,5 and 7 compared with those of day 1 after MV [H2O2 (μmol/L): 0.10±0.03, 0.06±0.03, 0.04±0.03 vs.0.19±0.14,IL-6 (ng/L):11.11±2.39,10.35±2.09,8.89±2.63vs. 14.45±6.03,all P<0.05].A significantly lower H2O2 level was observed on day 7 compared with that of day 3 (P<0.05).②A significantly higher H2O2 level in the non-survival group was observed on days 5 and 7 compared with that of day 1 (0.16±0.15,0.25±0.16 vs.0.05±0.03, both P<0.05).A significantly higher IL-6 level was observed on days 3,5 and 7 compared with that of day 1 (9.36±2.38, 10.55±2.33, 4.05±4.23 vs. 6.87±3.47, all P<0.05). The significantly higher H2O2 and IL-6 levels in non-survival group were observed on day 7 compared with those of days 3 and 5 (all P<0.05). ③The significantly lower H2O2 and IL-6 levels in non-survivors were observed on day 1 after MV compared with survivors (both P<0.05). There were no marked differences in levels of H2O2 and IL-6 between non-survivors and survivors on day 3 (both P>0.05). A significantly higher H2O2 level in non-survivors was observed compared with survivors on day 5 (P<0.05). In addition, the significantly higher H2O2 and IL-6 levels in non-survivors were observed on day 7 compared with survivors (both P<0.05). ④ The levels of H2O2 and IL-6 in EBC in survivors and non-survivors undergoing MV showed no correlation with acute physiology and chronic health evaluation Ⅱ (APACHEⅡ) and APACHEⅢ scores (both P>0.05). Conclusion The findings suggest that the levels of H2O2 and IL-6 in EBC are correlated with prognosis of patients undergoing MV, and it may prove to be useful in monitoring inflammatory response in the airway after MV as a guidance of therapy and prognosis in COPD patients undergoing MV.