The aim of this study was to investigate the possible antioxidant and anticancer activities of the essential oil from the leaves of Croton argyrophyllus Kunth (EOCA). In order to evaluate the antioxidant effect, two tests were performed: 1) in vitro lipid peroxidation activity, at the concentrations of 50, 100 and 200 µg/mL, with a reduction in malondialdehyde (MDA) values of 4.26 ± 0.15, 2.92 ± 0.16 and 1.61 ± 0.27 nmol EqMDA/mL, respectively; 2) activity against DPPH, at concentrations between 50 and 150 µg/mL, with IC50 187.61 µg/mL. For the evaluation of a possible anticancer activity of EOCA, the in vitro cytotoxic activity was first determined on cultured tumor cells, showing IC50 values of 14.81 µg/mL, 21.86 µg/mL and 32.79 µg/mL against SF-295, OVCAR-8, and MDA/MB-435, respectively. For tumor cell lines HCT-8 and HL-60, the IC50 values were > 50 µg/mL for both cells. Besides those, hemolytic assay, evaluation of in vivo tumor growth and systemic toxicological evaluation were performed, but no significant statistical change was observed. In conclusion, the EOCA has antioxidant activity and anticancer activity in vitro against cancer cell lines tested without in vivo antitumor activity.