There is variation in rooting capacity among the different species of Nothofagus. Lenga cuttings (N. pumilio) present an almost null answer to rooting, compared to raulí (N. alpina) and roble (N. obliqua). According to antecedents compiled in literature, the endogenous levels of indole acetic acid (IAA), hormone responsible for the formation of adventitious roots, vary depending on the levels of IAA oxidase activity. Based on these observations, the IAA oxidase activity was comparativily analyzed in cuttings from these three Nothofagus species. To quantify the enzymatic activity, a spectrophotometric test was carried out, measuring at 535 nm. The residual amount of IAA was determined by reference to a calibration curve. The enzymatic activity was expressed in IAA mM mg protein–1 hours–1. The results show that lenga presents a greater IAA oxidase enzymatic activity when compared to the other analyzed species (P< 0.05). These results would support at least partially the differences in the rootting capacity in Nothofagus species studys.