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ABSTRACT Hardening is the process of exposing seedlings gradually to field conditions. It improves seedling quality through several strategies, including stem bending and the use of plant regulators. Thus, the objective of the experiment was to quantify the physiological changes resulting from mechanical and chemical hardening in Hymenaea courbaril L. seedlings as a function of seedling growth stages. The experiment was conducted at Marechal Cândido Rondon, PR, in a shade house. The design used was a completely randomized, consisting of three treatments (control, methyl jasmonate and stem bending), with seven replications of 16 seedlings. At the end of the hardening treatments we quantified stem bending stiffness, lignin, phenolic compounds, loss of electrolytes and chlorophyll. The phenolic compounds quantified in the leaves increased with the application of both treatments in seedlings of stages I and II. Furthermore, mechanical hardening favored an increase in chlorophyll at all stages. H. courbaril seedlings from stages II and III would be the most recommended for hardening treatments. Mechanical hardening was the most suitable for Hymenaea courbaril L. seedlings.