Abstract Objectives The pathogenesis of COVID-19 infection is still not well clarified. In this regard oxidative stress and its relation to disease severity is one of the topics that need to be investigated. Aim This study was carried out to investigate the relationship between the oxidant stress and antioxidant system represented by total antioxidant capacity and clinical severity of COVID19 infection in pediatric age group. Methods The current cross-sectional study included 45 patients with COVID 19 PCR-proven infection admitted at the Children’s Hospital, Faculty of Medicine, Ain Shams University compared to 45 healthy age and sex matched control group. Detailed medical history, thorough examination and recording of all infection related laboratory parameters were done for each enrolled case. Measurement of total antioxidant capacity (TAC) in the serum of all studied patients and controls was done by ELISA. Results TAC levels were considerably lower in pediatric patients (median 24u/l, IQR 9-37u/l) compared to healthy individuals (median 90u/l, IQR 77-100u/l, p < 0.001) and the levels were statistically lower in severe cases compared to those with mild disease (p = 0.008). In this regard, 100% of controls showed normal TAC while only 31.1% from cases exhibited normal TAC levels and 68.9% of cases had low TAC levels. There was strong statistical significance between PICU admission and low TAC levels (p = 0.035). Additionally, the TAC showed negative correlation with the initial CRP of patients (r= -0.433, p = 0.003). There was also a significant inverse correlation between TAC and time needed for viral clearance (r=- 0.418, p = 0.004) as well as a significant positive correlation between body mass index z-score and TAC levels (r = 0.423, p value 0.004). Conclusion Total antioxidant capacity could serve as a novel prognostic marker of COVID -19 infection severity in pediatric patients.