Currently, there is evidence of deleterious effects of xenobiotic exposure (including herbicides, pesticides and plaguicides) in several animal species. Effects of glyphosate on organic systems such as respiratory and tegumentary system have been described; however, the effects of this kind of xenobiotics on immune system of non-target animals, including aquatic animals are as scarce as necessary. Dynamic and equilibrium alterations of the immune response could be eliciting impor- tant effects on ability of fish to survive in the environment challenge. This current work assessed the effect of glyphosate (Roundup ® ) and added surfactants (Cosmoflux ® 411F), on oxidative status of red-bellied pacu (Piaractus brachypomus) in a 14-day period of chronic sublethal exposure. It was evident that glyphosate Roundup ® as well as its mixture with sur- factant induce an increase on oxidative activity (oxidative stress) in exposed animals. These effects were higher in animal exposed to the mixture than Roundup ® alone, giving an important role of surfactant on the effect. In the same way, article approaches to pathophysiological support of these findings.