Objective To investigate the clinical significance of early lactate clearance rate in respect of the prognosis of patients with severe chronic obstructive pulmonary disease (COPD) . Methods A total of 108 COPD patients with respiratory failure were studied prospectively. The patients were divided into survival group ( n = 82) and the death group ( n = 26) , and the survival group further divided into the conventional treatment subgroup ( n = 55 ) and the invasive ventilation subgroup ( n = 27 ) . Arterial blood lactate, arterial gas analysis, APACHE Ⅱ score and the 6-hour clearance rate were measured before and 6 hours after treatment in 3 groups. The high lactate clearance rate group (n =71 ) was defined as a lactate clearance rate ＞ 10% , and the low lactate clearance rate group (n = 37) with a lactate clearance rate ＜ 10%. The correlation between 6-hour lactate clearance rate and prognosis in patients was analyzed. Results Compared the survival patients in invasive ventilation group with the death group, there were no statistical differences in arterial blood lactate, pH value, PaCO2, PaO2, oxygenation index and APACHE Ⅱ score before the treatment. The 6-hour lactate clearance rate in survival patients in conventional treatment group or invasive ventilation group was significantly higher than that in the death group (t =31.2, P＜0. 01; t =34.6, P＜0. 01, respectively), while there were no statistical differences in APACHE Ⅱ score and pH value between these 3 groups. Between the conventional ventilation treatment group and the invasive ventilation treatment group, there was no statistical difference in 6-hour lactate clearance rate ( P ＞ 0. 05 ) . There was no statistical difference in APACHE Ⅱ score between before treatment and after treatment in 3 groups. Mortality in high lactate clearance rate group (4. 2% ) was significantly lower than that in low lactate clearance rate group (62. 2% ) (x2 = 121.9, P ＜ 0. 01 ) .Conclusions The early (6h) lactate clearance rate could be used as a marker for evaluating the severity,therapeutic efficacy and prognosis of patients with severe COPD.