Introduction: Children who are critically ill typically suffer from a disease process that impacts many organ systems. To improve the outcome, these children are treated in a pediatric intensive care unit. The primary focus of intensive care medicine is the care of patients who are facing immediate life-threatening conditions. The aim of this study was to determine the acid- base status & electrolyte imbalance in critically ill ventilated infants. Methods: This was a prospective observational study and was conducted in the Department of Intensive Care Unit (ICU) of Bangladesh Shishu Hospital & Institute, Dhaka, Bangladesh during the period from January 2020 to December 2020. In our study, we included 50 critically ill ventilated young infants in ICU of Bangladesh Shishu Hospital & Institute. Results: In our study, we found that almost three fourth (74.0%) patients died and 13(26.0%) patients survived. Majority of our patients were ≤ 15 days and male. We found 22(59.5%) patients had PH level <7.25 in death group and 6(46.2%) in survival group and PH level ≥7.15 was (81.1%) in death group and 10(76.9%) in survival group. Before extubation & death metabolic acidosis was 19(51.4%) in dead group and 2(15.4%) in survival group. Significant relation was found between serum sodium level <135 and outcome of ventilated patients [p=0.039, OR=0.19(0.04-0.89)]. Imbalance of single & more than one electrolyte was found 43.24% & 56.76% in death group and 61.5% & 38.5% in survival group respectively. Conclusion: We found that arterial blood gas analysis & serum electrolytes level provide valuable information for correction of acid–base imbalance associated with a pathological condition. Electrolyte imbalance, regardless of the basic disease etiology, is a significant prognostic indicator that must be rapidly treated in critically ill children to get a good outcome.