Critically ill children admitted to the pediatric intensive care unit (PICU) from 75 to 166 per 100,000 children/year including respiratory diseases, infectious diseases, congenital diseases, and perioperative care. Early detection of disease severity in critically ill children uses the PELOD-2 score. Previous studies have shown that neutrophil lymphocyte ratio (NLR) can be used as a predictor of pediatric mortality and monocyte and lymphocyte ratio (MLR) to determine the severity of Klebsiella pneumonia infection. The aim of this study is to determine the correlation of NLR and MLR to PELOD-2 score in critically ill children in the PICU of Haji Adam Malik General Hospital. The research method is cross sectional analytic research from medical records, then documentation of PELOD-2 scores. The subjects were critically ill children from October to December 2022 according to the inclusion and exclusion criteria. Data were analyzed with the Spearman correlation test. Results: A total of 59 pediatric patients, the most was female 34 patients (57.6%). The mean age of the children was 6.23 years old. With the most indications was respiratory disease 22 people (37.3%). Spearman correlation test analysis showed that there was no significant correlation between NLR and MLR with PELOD 2 on the first day (p=0.316 and p=0.696) and MLR with PELOD 2 on the third day of treatment (p=0.077). However, a significant correlation was found between NLR and PELOD 2 in critically ill children on the third day of care (p=0.014). Conclusion: There was a significant correlation between NLR and PELOD-2 score on the third day of care. However, there was no correlation between first and third day MLR and first day NLR with PELOD-2 score.