ObjectiveTo evaluate the value of serum procalcitonin (PCT) levels for differentiating grampositive and gramnegative bacterial infection.Methods133 samples of blood, sputum, urine, or the others were performed bacterial culture, and serum PCT levels were measured and analyzed to find whether there was difference in PCT levels between grampositive and gramnegative bacteria infected patients.ResultsWhen bacteria were isolated from blood culture, serum PCT levels in patients with gramnagetive bacterial infection were obviously higher than that of grampositive group (［38.45±60.30］)ng/mL vs ［4.64±7.81］)ng/mL, P<0.001) ; According to receiver operating characteristic curve, if 5.61 ng/mL was taken as critical value, PCT sensitivity in the diagnosis of infection was 73.70%, and specificity was 81.80%. When sputum and the other samples were isolated bacteria, there was no statistical difference in patients’ serum PCT levels (P>0.05). PCT level in positive blood culture group was significantly higher than those of the other groups (P<0.001). ConclusionSerum PCT level is valuable to discriminate blood stream infection caused by gramnegative from grampositive bacteria, but the value to discriminate lung and the other local infection need to be further studied.