In the last several decades, exposure to pesticides has become a concern to environmental and human health. Many pesticides are environmentally persistent and are characterized by varying degrees of toxicity and adverse effects, including DNA damage. The present study was undertaken to evaluate the genotoxic potential of organophosphate pesticide fenthion in Wistar rats, as assessed by the comet assay. Adult male Wistar rats were treated with a solution of fenthion at a concentration of 40 mg/kg/day, administered intraperitoneally for 18 consecutive days. Rats were killed 24 hours after the last pesticide administration, and the comet assay was performed in peripheral blood cells. The comet assay results revealed that the damage index (19.29 ± 3.59 vs. 7.80 ± 2.25) and the damage frequency (17.00 ± 3.46 vs. 7.5 ± 2.46) found in fenthion-treated rats were significantly higher than those found in the control group (p = 0.001 and p = 0.0006, respectively). The results show that fenthion affects the DNA integrity of rat cells and may induce DNA damage in exposed organisms.