Marine beach shell deposits recording a pre-Holocene marine transgression have been found at the southern shore of the Beagle Channel, Isla Navarino, Chile. These shelly deposits were dated by AMS at 41,700 (14)C years B.P., which clearly indicates a Pleistocene age. A sample of wood underlying the marine deposits yielded an infinite age (>46.1 (14)C ka B.P.). If the date on the shells is considered as a minimum, infinite age, together with the elevation of these marine units above present mean tide sea level (at least 10 in a.s.l.) they may be considered as deposited during the Last Interglacial, of Sangamon age (Marine Isotope Stage -MIS- 5e) or during a younger phase of MIS 5. The fossil content of this unit is similar to the fauna living in this region today, supporting also an Interglacial palaeoenvironment interpretation. If this interpretation and the dating proposal are correct, this is the first reported record of Sangamon deposits in the Beagle Channel and the southemmost Last Interglacial site (MIS 5) in South America.