In this work, we applied seeded growth colloidal method to produce Au-FexOy dumbbells nanoparticles (DBNPs). The colloidal DBNPs were characterized and deposited on SiO2 to evaluate the effect of Au-FexOy interface on the catalytic activity in CO oxidation (CO+1/2O(2) -> CO2). In particular, we addressed the impact of redox pretreatments in the catalytic activity. Catalytic data showed that the catalyst was not very active after the first oxygen activation but after a reduction step there was a substantial increase in the catalyst activity. A detail characterization showed that DBNPs suffered great morphological and structural changes with the formation of core/shell Au-FexOy structures, in which the FexOy shells were irregular and presented lower crystallinity. The results suggest that the increase in catalytic activity was related to the formation of a more extended Au-FexOy interface after the pretreatments, thereby increasing the amount of active sites. (C) 2016 Elsevier B.V. All rights reserved.