Fipronil is an insecticide widely used in sugarcane crops in several areas of the world. In tropical areas, the application of this and other pesticides is intensified during the rainy season due the soil moisture, which coincides with the period of reproduction for many amphibian species. Since this pesticide can be easily incorporated into ephemeral ponds by leaching, it is possible that many neotropical amphibians are being affected by exposure to fipronil, specially during the initial stages of life when they are exclusively aquatics. This study aimed to evaluate the effects of the commercial formulation of insecticide fipronil (Regent®800WG) on antioxidant enzymes and development stages of tadpoles of Physalaemus nattereri at nominal concentrations of 0.5 and 1.5 mg/L. Activity of antioxidant enzymes catalase (CAT), glutathione-S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) was reduced in animals exposed to two tested concentrations of fipronil (0.5 mg/L and 1.5 mg/L), with similar response after two and seven days of exposure. Glutathione reductase (GR) activity was not altered after treatments. After seven days of exposure, an evident acceleration on stages of development was observed in animals exposed to the highest concentration of fipronil. This study conclude that the commercial formulation of fipronil (Regent®800WG) impair the antioxidant system of P. nattereri and accelerates the metamorphosis of these tadpoles, which could result in more vulnerable adults, promoting adverse consequences at population level.