ABSTRACT Mercury (Hg) is one of the most toxic heavy metals, and it is largely used in illegal gold extraction in Peru. We evaluated the tolerance to Hg in Paronychia microphylla Phil, Ambrosia artemisioides Willd and Croton ruizianus Müll. Arg. plants, using controlled concentrations (5, 10 and 80 mg Hg L-1). Two groups were identified according to the antioxidant enzymatic and bioaccumulation response, but the changes in the soluble protein suggest other tolerance mechanisms in the species. P. microphylla has an accumulator performance (BCF = 1.16 at 10 mg Hg L-1); in contrast, C. ruizianus has a exclusor behavior with low BCF and better antioxidant response. In that sense, the concentration of 5 mg Hg L-1 triggers the oxidative stress and increases the levels of malondialdehyde and proline, but when treatment concentration increases there is regulation in the antioxidant system. Among the three species, C. ruizianus Müll. Arg. has the better antioxidant response, but the lower bioaccumulation.