Objective: To explore the evaluation value of peripheral blood red blood cell distribution width (RDW), procalcitonin (PCT) and lactic acid for severity of neonatal septicemia (NS). Methods: A total of 132 children with NS admitted to the hospital were enrolled as the research objects between May 2019 and December 2022. According to neonatal critical illness score (NCIS), children were divided into non-critical group(>90 points, 94 cases) and critical group (70-90 points, 38 cases). The levels of peripheral blood RDW, PCT and lactic acid in the two groups were compared. The diagnostic value of the above three indexes for critical NS was evaluated by receiver operating characteristic (ROC) curves, and their correlation with disease severity was analyzed by Spearman analysis. Results: The proportion of gestational age <37 weeks in critical group was higher than that in non-critical group, while birth weight was lower than that in non-critical group (P<0.05). The levels of peripheral blood RDW, PCT and lactic acid in critical group were higher than those in non-critical group (P<0.05). The results of ROC curves analysis showed that area under the curve (AUC) values of RDW, PCT, lactic acid and combined detection for evaluating critical NS were 0.844, 0.645, 0.643 and 0.874, respectively(P<0.05). Spearman analysis showed that RDW, PCT and lactic acid were positively correlated with disease severity in NS children (P<0.05). Conclusion: The peripheral blood RDW, PCT and lactic acid are closely related to disease severity in NS children. Clinically, combined detection of the three indexes can be applied to evaluate disease severity in NS children. [ABSTRACT FROM AUTHOR]