Heavy metal environmental contamination severely limits crop growth and productivity due to its high phytotoxicity. One of the primary mechanisms by which heavy metals affect plants is the generation of reactive oxygen species, which can damage biomolecules or function as signaling molecules that activate antioxidant defenses. Antioxidant compounds play a crucial role in mitigating oxidative damage and alleviating the negative effects on plant physiology and performance. This chapter presents a method for extracting phenolic compounds and characterizing them using liquid chromatography to assess heavy metal-induced phytotoxicity. Phenolic profiling is a useful approach to evaluate plant antioxidant capacity under heavy metal stress and to identify compounds with relevant role in stress response.