Background: Malnutrition in critically ill children is a significant concern with implications for prognosis and pediatric intensive care unit (PICU) outcomes. Early detection of malnutrition plays a crucial role in timely intervention and improved patient outcomes. This study aimed to identify the role of serum prealbumin in early detection of malnutrition in critically ill children and its relation to prognosis. Methods: This prospective cross-sectional study was conducted on 50 critically ill children from both sexes, aged 1 month to 18 years, admitted for at least 48 hours to a tertiary PICU. Nutritional status was assessed using various anthropometric measures, including weight, height, Body Mass Index (BMI) and mid-upper arm circumference (MUAC). Serum prealbumin levels were measured using immunoprecipitin analysis. Results: The age ranged from 1 month to 16 years. Twenty-seven (54%) patients were males, and 23 (46%) patients were females. Undernourished patients had significantly lower prealbumin levels and prealbumin z-scores compared to well-nourished patients. Prealbumin z-score is a significant predictor of malnutrition in the study participants (AUC: 0.663, p 0.037), at a cut-off value of ≤ 15.2mg/dl, it can predict malnutrition with a sensitivity of 43.5% and specificity of 74.1%. Conclusion: Serum prealbumin levels can serve as an early indicator of malnutrition in critically ill children. Lower prealbumin levels and prealbumin z-scores were associated with undernourishment.