Abstract: OBJECTIVE To explore diagnostic significance of early procalcitonin(PCT) levels between gram-positive and gram-negative bacteria, as well as its identification value in pathogenic bacteria species. METHODS The positive cases of blood culture in the Xuchang Central Hospital Affiliated to Henan University of Science and Technology between May 2014 and April 2019 were selected and 460 copies of the medical records were obtained after screening. Among them, 360 copies were gram-negative and 100 copies were gram-positive bacteria. Serum PCT levels (<12 h) before or after haemospasia for blood culture was recorded. A receiver operating characteristic(ROC) curve analysis was used to discriminate gram-negative from gram-positive bloodstream infections. The diagnostic value of early PCT levels at clinical common gram-negative bacteria species and gram-positive bacteria species(n=4 each) were compared. RESULTS PCT levels of gram-negative bacteria group7.42(1.51-33.04)was significantly higher than gram positive group0.70(0.24-3.66). The area under the ROC curve was 0.749, P<0.01. When the cut-off for PCT was 1.88 ng·mL^-1, the sensitivity and specificity of gram-negative bacteria infection was 73.3% and 75.0%, respectively. Among gram-negative bacteria, early PCT level of Pseudomonas aeruginosa group was significantly higher than Escherichia coli group(P<0.01), Klebsiella pneumoniae(P<0.01) and Acinetobacter baumannii group(P<0.01). Among gram-positive bacteria, early PCT level of Streptococcus group was significantly higher than coagulase negative Staphylococcus group(P<0.05). There was no statistical difference among other groups. CONCLUSION PCT level in early stage of bloodstream infection has significant effect on the diagnosis of gram-positive bacteria and gram-negative bacteria and plays a supporting role in identification for pathogenic bacteria species.