The aim of the study was to assess the level of selected systemic oxidative stress parameters during the first week of orthodontic treatment with fixed appliances. Fifty-four males with malocclusion and having a similar lifestyle were randomized using a computer based procedure and allocated to either the treatment group (TG; n=27;24.6 ± 1.7 years) or control group (CG; n=27;24.7 ± 1.7 years). Capillary blood was collected at baseline and 6 hours, 24 hours, and 7 days after archwire insertion. At the same time points, capillary blood was retrieved in the CG. In order to determine the oxidative stress, both the reactive oxygen species (ROS) formation and the antioxidative defense (AD) potential were measured using the ROS testing and oxygen free radicals defense (equivalent to antioxidant defense) testing, respectively, by a blinded operator. The ratio between ROS and AD (ROS/AD) was calculated and data were analyzed using nonparametric tests. No drop-outs or harms were detected. At baseline, neither ROS (1.54 [1.22; 2.12] and 1.74 [1.40; 2.01] for the TG and CG, respectively), AD (1.19 [0.66; 1.50] and 1.19 [0.57; 1.42] for the TG and CG, respectively), nor ROS/AD levels were significantly different (p>0.05). After 24 hours, the ROS level significantly increased in the TG (2.05 [1.71; 2.26]) and was higher compared to the CG ROS level (1.67 [1.29; 1.95]; p=0.025), while for the AD level, no marked between and within group differences were detected. A notable change of ROS/AD ratio was observed over time only within the TG (p=0.026). Moreover, a significantly higher ROS/AD ratio was detected 24 hours after archwire insertion in the TG compared to the CG (2.69 [1.44; 3.89] and 1.79 [1.45; 2.35], respectively), followed by a decrease. Orthodontic treatment with fixed appliances might induce systemic oxidative stress in the short-term, since ROS levels and ROS/AD levels are normalized within 7 days after archwire insertion.