<p>We investigated the phytoremediation potential of <i>Senna occidentalis</i> L., a pantropical plant associated with tolerance to heavy metal-contaminated soils around mining sites. <i>S. occidentalis</i> seedlings were exposed to cadmium chloride (CdCl₂) and sodium arsenate (Na₃AsO₄) (200, 300, and 400&#xa0;mg L⁻¹) under greenhouse conditions. Arsenic treatment had more toxic effects than cadmium on <i>Senna</i> physiology. Regardless of the concentration of arsenic applied, the biomass decreased by 50% compared to control and cadmium-treated plants. Higher concentrations of Cd and As (400&#xa0;mg L⁻¹) resulted in a 50% reduction in chlorophyll content. Proline and hydrogen peroxide levels were higher in arsenic-treated plants than in controls and cadmium-treated plants, indicating an enhanced stress response when exposed to arsenic. When heavy metal content was measured, there was a significant accumulation of arsenic in the leaves (&gt; 20&#xa0;ug g⁻¹), stems (&gt; 40&#xa0;ug g⁻¹), and roots (&gt; 400&#xa0;ug g⁻¹), indicating that arsenic in these tissues was responsible for the profound changes in biomass, proline, and hydrogen peroxide contents. In contrast, although significant, there was less cadmium uptake by <i>Senna</i>, and tolerance can be seen, which was reflected by normal biomass, proline, and hydrogen peroxide levels. High translocation of metals from soil into roots and low translocation from root to shoot tissues suggest the potential for <i>S. occidentalis</i> for phytostabilization of arsenic- and cadmium-contaminated soils.</p>