Objective To study the value of serum procalcitonin(PCT) to the early diagnosis of sepsis .Methods From June 2014 to June 2015 ,a total of 686 cases were enrolled in this retrospective study .PCT tests were assayed within 2 days of bacterial culture .Results In this study ,56 cases ,67cases ,and 567cases were classified into the positive blood culture group ,positive body fluid culture group ,and negative all culture group ,respectively .Median PCT values were 4 .26 2 .78 ,0 .46 ng/mL ,respectively .Me-dian PCT values in the gram-positive bacterial culture group and gram-negative bacterial culture group ,respectively ,were 2 .35 and 4 .56 ng/mL .Median PCT values in the positive hydrothorax culture group ,positive ascites culture group ,and positive bile culture group ,respectively ,were 1 .91 ,5 .23 ,3 .64 ng/mL .In all ,Median PCT values of 47 cases of sepsis and 16 cases of severe sepsis were 5 .32 and 10 .25 ng/mL ,respectively .Conclusion PCT level is correlated with the severity of sepsis ,pathogenic bacteria type ,and the site of infection ,and can be used in the early diagnosis of sepsis .