<b><i>Background:</i></b> Erythropoiesis-stimulating agents (ESAs) are used to treat anemia in CKD. Erythropoietin resistance index (ERI) is a useful tool used to evaluate the response to ESAs. In this study, we aimed to evaluate the causes of high ERI in children undergoing peritoneal dialysis (PD). <b><i>Method:</i></b> Patients who had been on PD for at least 1 year were included in this retrospective study. Demographic characteristics, residual kidney function (RKF), adequacy of dialysis, peritoneal glucose exposure, the number and reason for hospitalization, and medications were recorded. Anemia and laboratory parameters that may affect anemia were noted by taking the average of laboratory values in the last follow-up year (time-averaged). The weekly ESA dose was proportioned to the annual average hemoglobin value and body weight to calculate the ERI in terms of U/kg/week/g/dL. <b><i>Results:</i></b> A total of 100 patients were included in the study. The mean ESA dose and ERI value were 119.8 ± 66.22 U/kg/week and 13.01 ± 7.52 U/kg/week/g/dL, respectively. It was determined that the patients <5 years of age have very high ERI value, and these patients need 2 times more ESA than those >10 years of age. Absence of RKF, large number of hospitalization, and ACEI use were also found to affect the ERI value negatively. <b><i>Conclusion:</i></b> We demonstrate that the most important factor affecting ERI value is young age. We also reveal that absence of RKF, large number of hospitalization, and ACEI use are also important variables affecting the ERI value.