Red seaweed Gracilaria mammillaris from the Colombian Caribbean coast were investigated as source of extracts with antioxidant activity (AA), by means of supercritical CO2 extraction with ethanol as co-solvent. A central composite design was used to investigate the effects of pressure (10, 20 and 30 MPa), temperature (40,50 and 60 degrees C), and co-solvent concentration (2, 5 and 8%) on the extraction yield, AA, and total content of phenols and carotenes. The obtained extracts were compared with those produced using Soxhlet extraction at reduced pressure. The AA of samples was evaluated by determining their capacity for protecting an edible oil against oxidation, upon accelerated oxidation trials. The extracts obtained at 30 MPa, 60 degrees C and 8% co-solvent showed the highest AA, inhibiting in 42.1% the formation of TSARS after six days of accelerated oxidation. These results indicate that red seaweed G. mammillaris could be a promissory source of extracts with AA. (C) 2017 Published by Elsevier B.V.