Over the last 70 years, introduced beavers (Castor canadensis) have been successful in establishing and modifying the landscape of southernmost Patagonia. Habitat availability and lack of large carnivorous predators have contributed to this success. The Fuegian culpeo fox (Pseudalopex culpaeus lycoides) is an endangered subspecies and the largest native predator found in Tierra del Fuego Island. The predatory behavior of a culpeo towards a beaver was studied by analyzing a video footage recovered by tourists, and consumption of beaver was documented with camera traps. An ethogram of the predatory behavior sequence was developed and true durations and percentage of time allocated to each behavior were analyzed. The "capture" and "watch" behaviors had the highest durations within the predatory sequence (61.83 and 42.61 s, respectively), while "rest" was the most frequent maintenance behavior observed (93.82 s). The culpeo may provide the only natural population control for beavers, although up to date, there is no evidence to confirm this ecological role. Based upon photos from camera traps, we confirm the occurrence of fox feeding on beavers. This is the first description of the stages of the interaction between a Fuegian culpeo fox and a North American beaver under natural conditions. We discuss the ecological implications of this interaction.