The use of herbicides is constantly being adopted in developing countries who need to increase productivity in the agricultural sector. The world market for herbicides grew 39% between 2002 and 2011 and predicted a growth of 11% in 2016. The Paraquat® is herbicide with biological activity used worldwide. The present work had as objective to examine the respiratory system of rats exposed to paraquat. Wistarrats, with body weight of 225±25 g were used in this study. The animals were randomly divided into three groups, a group in which it was administered of saline (C), other group were administered paraquat to 10 mg/kg (P10), and a third group was administered paraquat to 30 mg/kg (P30), intraperitoneally. All concentrations used are considered environmentally relevant. The values of the airway resistance (?_??? ), tissue elastance (??), tissue resistance (??) and hyperresponsiveness of the airway smooth muscles of the animals, were statistically significant. In conclusion, ours results demonstrated the harmful character that exposure to paraquat can cause in the respiratory system of rats. More detailed studies are required that can quantify the level of exposure that the population undergoes when eating some foods, which may present remnants of this pesticide in its composition.