Introduction: Patients resuscitated after enduring cardiac arrest (CA) experience post-cardiac arrest syndrome, which mimics the physiologic derangement consistent with observations of severe sepsis. The delta neutrophil index (DNI), which reflects a fraction of circulating immature granulocytes, has been reported to be strongly associated with increased mortality in systemic inflammation, also in adult patients after CA. However, pediatric CA is different from adult CA in etiology or early pathophysiology. In this study we evaluated the prognostic significance of the DNI in terms of early mortality after CA in children. Methods: We retrospectively identified consecutive patients (≤18 years) with CA who received chest compression for ≥2 min from January of 2012 to January of 2018. Patients who survived at least 24 h after undergoing chest compression were included in the analysis. The DNI was determined on each day following the incidence of CA. The outcome of interest was the 30-day mortality. Results: A total of 85 patients who had a CA were included in the study (survival group; n=55, non-survival group; n=30). The median value of the DNI on day 1 (24 hours after CA) was 1.4% (interquartile range [IQR] 0-4.7%) in the survivor group, and 15.1% (IQR 6.7-28.7%) in the non-survivor group. The difference was statistically significant ( P < 0.001). The receiver operating characteristics analysis revealed a cut-off that predicted a 30 day-mortality, was a DNI on day 1 > 4.7% (area under the curve 0.816; 95% CI (0.713 to 0.895); P < 0.001). The Kaplan-Meier survival analysis revealed, the probability of survival was significantly lower in patients with DNI > 4.7% on day 1 (log-rank test; P < 0.001). Conclusions: The DNI level can be considered a useful indicator for predicting early prognosis in pediatric cardiac arrest patients