Introduction: Acute kidney injury (AKI) was a frequent complication after open heart surgery, especially in paediatric patients < 2 years old and had been related with increased mortality and adverse renal outcomes. This study aimed to determine the incidence of AKI post open heart surgery in paediatric patients and its relation with duration of cardiopulmonary bypass (CPB) and patient's age in Indonesia's tertiary national hospital. Methods: This was a cohort retrospective study, using medical records and cardiac ICU chart data of 195 paediatric patients who underwent open heart surgery from June 2014 - June 2015 in Integrated Cardiovascular Center Cipto Mangunkusumo hospital. After ethical approval from Research Ethics Committee, data was collected and sorted by inclusion and exclusion criteria. AKI was diagnosed based on RIFLE criteria. Data was analyzed by chi-square and multivariate analysis (SPSS software 22.0 version). Results: Incidence of AKI post open heart surgery in paediatric patients was 36.4%. Duration of CPB > 60 min had a significant correlation with increased incidence of AKI (p 0.043; RR 1.248). Patient's age (≤ 2 years old) also had a significant correlation with increased incidence of AKI (p<0.001; RR 2.431). Multivariate analysis results showed that both the duration of CPB and the patient's age were significant risk factors of AKI (OR 2.951, OR 5.371). Conclusion: Incidence of AKI post open heart surgery in paediatric patients was 36.4%. Duration of CPB duration (> 60 min) and patient's age (< 2 years old) were significant risk factors of AKI. © Bali Journal of Anesthesiology 2018.