Introduction: Perforated appendicitis (PA) in children is associated with a considerable risk for postoperative complications (POCs) such as wound infection and intra-abdominal abscess. The aim of this study was to determine the diagnostic accuracy of hematological parameters in the early POC detection in children after PA surgery. Materials and Methods: The study enrolled 71 patients with PA divided into two groups: 14 patients with POC (POC+ group) and 57 patients without POC (POC− group). Clinical and hematological parameters were followed preoperatively, prior to the surgery (PRO) and postoperatively on day 2 (POD2) and day 4 (POD4). Results: The POC+ group had longer duration of higher axillar temperature as well as extended intensive and inpatient care. This group also had a significantly lower absolute neutrophil count ratio between POD2 and POD4. According to the receiver operating characteristic curve analysis, relative neutrophil count on POD4 higher than 71.8% and the ratio of absolute neutrophil count between POD2 and POD4 lower than 44.5% were found to be useful for predicting POC. Conclusion: Absolute neutrophil count ratio between POD2 and POD4 and relative neutrophil count at POD4 could be efficient in identifying children at higher risk of developing POC after PA surgery.