Abstract: Objective To investigate the clinical significance of lactate, procalcitonin(PCT)combined with C reactive protein(CRP)interpretation in judgment of disease condition in premature infants with late-onset sepsis. Methods Totally 42 premature infants without infection were selected as control group, and 107 premature infants with late-onset sepsis were selected as infection group. Lactate, PCT, CRP, platelets(PLT)and white blood cell count(WBC)in serum were determined after hospital admission. According to assessment result of Neonatal Critical illness Score(NCIS), the infants in infection group were divided into group A(non critical cases, n=30), group B(critical cases, n=34)and group C(extremely critical cases, n=43). The significance of lactate, PCT and CRP in the evaluation of premature infants with late-onset sepsis was analyzed. Results Receiver-operating characteristic(ROC)curve analysis showed that the best cut-off points of CRP, PCT and lactate for early diagnosis of sepsis were 10.05 mg/L, 0.53 ng/mL and 2.70 mmol/L respectively, area under curve(AUC)was 0.889, 0.884 and 0.695 respectively, and AUC of combination of three indicators was 0.941, which revealed that the sensitivity and specificity of the combined detection of the three were indicators were significantly higher for diagnosis of premature infants with late-onset sepsis. The levels of lactate, PCT and CRP in group C were significantly higher than those in group B and A, and the levels of lactate, PCT and CRP in groupB were significantly higher - than those in group A(P<0.05 or P<0.01). The level of PLT in group C was significantly lower than that in group B and A, and the level of PLT in group B was significantly lower than that in group A(P<0.05 or P<0.01). There was no significant difference in the level of WBC among the three groups(P>0.05). Conclusion For premature infants with late-onset sepsis, the combination of lactate, PCT and CRP can earlier and accurately evaluate the disease condition to guide clinical treatment.