Abstract: Background: Nephrotic Syndrome (NS) is characterized by heavy proteinuria that leads to loss of significant amounts of thyroid hormones. Reactive Oxygen Species (ROS) seem to play an important role in the etiopathogenesis of protienuria in nephrotic syndrome. Objective: Evaluation of thyroid functions, oxidative stress and antioxidants in children with nephrotic syndrome. Materials and Methods: The present study was carried out at Al-Azhar University Hospital, Damietta during the period from March, 2015 to February, 2016. The study included 30 Egyptian children with steroid responsive nephrotic syndrome in relapsing phase and remission phase (Cases) and other 30 healthy Egyptian children (Control group). Venous blood was collected for the estimation of SOD activity, MDA, glutathione-S-transferase (GST) and estimation of thyroid hormones FT3, FT4 and TSH. Results: Serum FT3 and FT4 was significantly lower in patients with relapse (2.84±0.74 and 3.14±1.34, respectively) in comparison to remission (8.1±2.64 and 16.75±3.69, respectively) and control group (8.97±1.95 and 18.34±4.68, respectively). However, there was significant increase of TSH in patients with relapse (6.7±2.4) in comparison to remission (2.6±1.8) and control group (2.4±1.2). The SOD and glutathione-S-transferase levels were significantly decreased in patients with relapse (5.24±2.17 and 2.14±1.27, respectively) in comparison to remission (7.14±1.68 and 3.15±0.96, respectively) and control group (7.69±2.43 and 3.54±1.83, respectively). However, there was significant increase in MDA levels in patients with relapse (8.4±2.74) in comparison to remission (2.1±1.22) and control group (1.8±0.86 ). Conclusion: Nephrotic syndrome can loss significant amounts of thyroid hormones along with protein in urine. Increased Reactive Oxygen Species (ROS) as MDA and decreased antioxidants as SOD and GST may be related to the pathogenesis of proteinuria in NS.