Burn is a systemic injury affecting the entire organism according to its etiology and severity. The aim of this study was to investigate plasma AOPP levels before and after treatment of second- and third-degree thermal burn patients and determine the changes in this parameter, and also, to find out the relationship between AOPP level and hospitalization period and total body surface area (TBSA). The study material consisted of pediatric patients with the complaint of second- and third-degree thermal burns aged between 1 and 18 years, with a burn area exceeding 10%. Blood samples were taken twice before and after treatment. AOPP level in blood plasma was measured in ELISA. It was observed that in the second-degree thermal burn group, AOPP level was 25.85 ± 2.82 ng/ml before the treatment decreased to 22.16 ± 3.62 ng/ml after treatment, whereas in the third-degree thermal burn group before the treatment AOPP was 25.96 ± 3.49 ng/ml, and after the treatment dropped to 21.70 ± 3.79 ng/ml, decreases were significantly important (P < .05). There was no statistically significant difference between the two groups in terms of AOPP levels (P > .05). Correlation analyses in the second- and third-degree thermal burn group did not show any correlation between AOPP levels and burn area and length of hospitalization period. As a result, AOPP level has been studied, for the first time, in burn cases. In both groups, the level of AOPP increased due to oxidative stress before treatment and decreased after treatment.