Invasive exotic species of mammalian predators represent a major cause of vertebrate animal extinctions on islands, particularly those that lack native mammalian carnivores. In 2001, the American mink (Mustela vison) was recorded for the first time on Navarino Island, in the Cape Horn Biosphere Reserve (55° S) in Chile, representing the southernmost population of mink worldwide. In order to assess its potential impact on native fauna, we studied its diet on Navarino Island, as part of an integrative management program on invasive species. Over a three-year period (2005-2007) we collected 512 scats in semi-aquatic habitats: marine coasts, riparian and lake shores. Overall, the main prey was mammals (37 % biomass), and birds (36 %), followed by fish (24 %). Over the spring and summer, mink consumed significantly more birds, whereas mammals constituted the main prey over the autumn and winter when migratory birds had left the area. Among birds, the mink preyed mainly on adult Passeriformes, followed by Anseriformes and Pelecaniformes, caught as chicks. Among mammals, the exotic muskrat (Ondatra zibethicus) was the most important prey, and together with the native rodent Abrothrix xanthorhinus it accounted for 78 % of the biomass intake. For an integrated management of invasive exotic mammal species on Navarino Island and in the Cape Horn Biosphere Reserve it is important to further research interactions established here among the various introduced mammals, and to initiate immediate control of the mink population in its initial stage of invasion.