Abstract: Objective:To observe the significance of the lactic acid level, lactic acid clearance rate, and the acute physiology and chronic health evaluation Ⅱ(APACHEⅡ) score in evaluating the clinical efficacy and prognosis of critically ill patients.Methods:The serum lactic acid level and the clearance rate were monitored, and the APACHE Ⅱ score was determined in the first 24 hours in 68 critically ill patients in the intensive care unit(ICU).The patients were divided into survival group, death group, high lactic acid clearance group and low lactic acid clearance group.Results:The 6 h lactic acid clearance rate of the survival group was significantly higher than that of the death group(P<0.01);the APACHEⅡ score and mortality rate of the patients with high lactic acid clearance was significantly lower than those with low lactic acid clearance(P<0.01).Conclusions:The lactic acid clearance rate in critically ill patients may indicate the severity of the illness and are worth clinical concerning.