A 2.7 m thick mid-Holocene sedimentary succession composed of alluvial fan and marine beach deposits is exposed at 14.4–17.1 m above sea level (a.s.l.) on the south-eastern coast of Potter Peninsula, King George Island (South Shetland Islands, Antarctica). The raised marine beach deposits contain a subfossil assemblage that includes remains of Adélie (Pygoscelis adeliae) and gentoo (P. papua) penguins, skua (Catharacta sp), seals (elephant seal Mirounga sp), and seaweed fragments. The palaeontological and palaeogeographical evidence allows us to infer that penguin rookeries were active on high cliffs of the Potter Peninsula during the marine beach sedimentation, which is dated to c. 4540–4450 reservoir-corrected 14C yr BP on the basis of radiocarbon dating on penguin bones. The data presented in this paper are in agreement with the Holocene palaeoenvironmental chronology known from Potter Peninsula, and suggest that marine birds and seals inhabited the coastal areas of King George Island probably during a mid-Holocene period of seasonally open marine conditions, which may coincide with a cooling period around Antarctica estimated from ice core records between 8000–4000 yr BP that preceded the “climate optimum” in the Antarctic Peninsula (4000–3000 yr BP).