Dietary and serum total antioxidant capacity (TAC) are considered appropriate tools for investigating the potential health effects of dietary antioxidants consumed in mixed diets. The aim was to analyze the impact of a dietary intervention on macronutrient intakes and to evaluate the improvement on oxidative status after weight loss (WL) by measuring dietary and serum TAC, and urinary F2-isoprostane levels as markers of oxidative stress. Forty-four overweight/obese children (mean age 11.5 years) were enrolled to undergo a 10-week WL program. They were dichotomized at the median of body mass index-standard deviation score (BMI-SDS) change, as high (HR) and low responders (LR) after intervention. Subjects were prescribed with a fixed full-day meal diet, calculated according to their basal metabolic rate and physical activity levels. A validated food-frequency questionnaire was used to retrospectively calculate TAC and daily nutrient intake. The HR subjects were able to reduce anthropometric indices and to improve lipid and glucose profile. They also significantly diminished fat intake (p¿=¿0.013). Moreover, baseline serum TAC values did significantly predict the reduction in urinary F2 isoprostane (B¿=¿-0.236 (-0.393 to -0.078); p¿=¿0.014) in the HR group after the WL program. Notably, changes in dietary TAC after the treatment were associated with a decrease in body weight after the 10-week intervention (B¿=¿-2.815 (-5.313 to -0.318), p¿=¿0.029) in the HR group. The -¿SerumTAC/¿DietaryTAC and the -¿F2Isoprostane/¿DietaryTAC ratios revealed that the relationships between oxidative markers and antioxidants dietary intake were more favorable in the HR than in the LR group. Conclusion: Our study showed that a 10-week WL program was able to reduce adiposity indices in obese children. Moreover, after the intervention changes in dietary TAC and WL were significantly associated. Our result suggests that specific food with a high TAC content (such as fruits, vegetables, and legumes) could be recommended to improve WL.