ABSTRACT. At present, the use of nanoparticles is a controversial topic, especially when analyzing their effects in human tissues. Nanoparticles (NPs) can cause oxidative stress by increasing membrane lipids peroxidation and reactive oxygen species, and decreasing intracellular glutathione. Oxidative stress plays an important role in cell signaling ) and silicon oxide (SiO 2 ) NPs dissolved in saline solution were administered orally to the rats. Cardiac puncture was performed to extract peripheral blood for genotoxic analysis. DNA fragmentation for lymphocytes was performed. Control rats showed a fragmentation percentage of 11.20 ± 2.16%. Rats exposed to SiO 2 and Fe 2 O 3 NPs for 24 h showed statistically significant differences in DNA fragmentation percentages as compared with that of the control group. A lineal dose-response correlation between genotoxic damage and exposure to SiO 2 and Fe 2 O 3 NPs was found (r 2 = 0.99 and 0.98 for SiO 2 and Fe 2 O 3 , respectively). In conclusion, we found that exposure to Fe 2 O 3 and SiO 2 NPs can cause DNA fragmentation in lymphocytes in a dose-dependent manner.