Abstract: Objective: To study an effect of early lactate clearance rate on evaluation of prognosis in severe pneumonia patients. Methods: In 42 severe pneumonia patients, the scores of acute physiology and chronic health evaluationⅡ(APACHEⅡ) were evaluated, the lactate levels of arterial blood were measured before treatment and 6 hours after treatment, and the lactate clearance rate at treatment 6 h were calculated. Forty-two severe pneumonia patients were divided into the survival group and the dead group, the high lactate clearance rate group and the low lactate clearance rate group, and the differences were analyzed. Results: Before treatment, the lactate levels of arterial blood were 2.1～7.1（5.3）mmol/L in the survival group and 2.3～7.6（5.7）mmol/L in the dead group respectively(P>0.05), and the scores of APACHEⅡ were 11～29（20）in the survival group and 16～30（23）in the dead group respectively (P>0.05). At 6 hours () after treatment, the lactate clearance rate was significantly higher in the survival group than in dead group (P<0.01). Before treatment, the lactate levels of arterial blood were 2.3～7.1（5.5）mmol/L in high lactate clearance rate group and 2.1～7.6（5.8）mmol/L in low lactate clearance rate group respectively, the scores of APACHEⅡ were 11～30（21）in high lactate clearance rate group and 16～29（24） in low lactate clearance rate group respectively, and there were no significant differences in the lactate levels of arterial blood and the scores of APACHEⅡ between two groups(P>0.05).The mortality (25%) in the high lactate clearance rate group was significantly lower than in the low lactate clearance rate group(56%, P<0.01). Conclusion: The early lactate clearance rate might be a marker on evaluation of prognosis in severe pneumonia patients.