Background: Tc-99m DMSA scintigraphy is a commonly used imaging modality in the pediatric population. The radiopharmaceuticals which have the effects of ionizing are used in this method. This study aimed to investigate the impact of the Tc-99m DMSA scan on renal oxidative stress and mononuclear leukocyte DNA damage. Methods: Twenty-seven patients who performed Tc-99m DMSA scintigraphy were included in this study. Three ml heparinized blood samples were taken just before, during, and after a week from the scintigraphy. Mononuclear leukocyte(MNL) DNA damage, total antioxidant status (TAS), and total oxidant status(TOS) were measured in blood samples. The oxidative stress index (OSI) was calculated. The spot urine samples were taken from each patient before and within three days after performing the scintigraphy. TAS/Creatinine(TAS/Cr), TOS/Creatinin(TOS/Cr), and N-acetyl-glucosaminidase/creatinine(NAG/Cr) levels were measured in urine samples. OSI was calculated. Results: There was no statistically significant difference in the values of TAS, TOS and OSI studied in serum samples between controls and study group(p=0.105, p=0.913, and p=0.721, respectively). There was no statistically significant difference in the levels of TAS/Cr, TOS/Cr, NAG/Cr, and OSI which were studied in urine samples before and after scintigraphy scan(p=0.381, p=0.543, p=0.129 and p=0.08 respectively). The levels of DNA damage were increased only after the performance of the scintigraphy scan and decreased a week later(p<0.05). Conclusions: The effect of Tc-99m DMSA scintigraphy is insufficient to create oxidative damage, but it can cause DNA damage via the direct impact of ionizing radiation which can be repaired again in a short time. Keywords: Tc-99m DMSA, DNA damage; reactive oxygen species; renal tubular injury; children