Аннотация:COVID-19, OXIDATIVE STRESS INDEX, CHILDREN, ADOLESCENTS, POLYMERASE CHAIN REACTIONАННОТАЦИЯ: The aim of our research was to assess the intensity of oxidative stress (OS) in children and adolescents with COVID-19 using the oxidative stress index (OSI). Methods and Results: The study was conducted between May 2020 and March 2021. The main group included 17 children and adolescents [8(47.1%) boys and 9(52.9%) girls; mean age of 12.35±4.01 years] with diagnosed COVID-19 infection (mild to moderate course) selected as a result of the primary diagnostic examination from among those admitted to hospitalization at the Irkutsk Regional Infectious Diseases Clinical Hospital. The control group included 17 healthy children and adolescents (average age of 12.35±4.01 years) matched by copy-pair type. The obtained data indicated statistically significant differences in a number of parameters between children and adolescents with COVID-19 and the control groups. We found statistically significant higher levels of LPO products (CDs, P <0.0001; KD and CT, P =0.006; and TBARs, P =0.013) in the study group than in the control group. Among AOD system parameters, the levels of retinol ( P =0.015) and reduced glutathione ( P =0.048) and SOD activity ( P <0.0001) were statistically lower in the study group than in the control group. The OSI level was significantly greater (by 8.5 times, P =0.028) in the study group than in the control group, which confirms the development of antioxidant deficiency in COVID-19. Conclusion: The results of the assessment of OSI in children and adolescents with COVID-19 indicate insufficient activity of some critical components of AOD and a shift of the redox balance toward pro-oxidant factors, which can have extremely negative consequences in the development of the disease. In this regard, we recommend carrying out corrective measures to stabilize LPO/AOD parameters by including drugs with antioxidant properties in the treatment complex.