The synthesis of copper oxide nanoparticles (CuO NPs) using yerba mate extract proved to be a sustainable and efficient approach, eliminating the need for aggressive precipitating agents and reducing environmental impact. Characterization confirmed that crystalline CuO NPs were obtained, with an average crystallite size of 22.9 nm and a hydrodynamic diameter of 63.41 nm. The conversion yield was strongly influenced by the reaction temperature, reaching a maximum of 26.75% at 80°C and 2 g of copper nitrate. The proposed synthesis mechanism indicated the formation of an intermediate complex between copper and yerba mate bioactives, the calcination of which resulted in the formation of nanoparticles. FTIR, XRD and UV-Vis spectroscopy analyses corroborated the presence of pure CuO, while zeta potential analysis (-13.5 mV) indicated moderate colloidal stability.