Oxygen-isotope analysis of well-preserved macrofossils from the Santonian-Campanian of James Ross Island and the Maastrichtian of Vega Island, Antarctica, indicates that cool high-paleolatitude temperatures prevailed during the Late Cretaceous and suggests that cooling occurred between the Santonian-Campanian and the Maastrichtian. Although more than 50% of the material showed diagenetic alteration, 52 unaltered aragonite and calcite samples were analyzed. Mean δ18O and calculated paleotemperature values were -0.23‰ and 13.6 °C, respectively, for the Santonian-Campanian, and 0.66‰ and 11.7 °C, respectively, for the Maastrichtian. In conjunction with recent Late Cretaceous paleoclimatic data from high northern paleolatitudes, these data indicate the presence of cool polar regions with broad climatic zonation during the Late Cretaceous. This may have partly controlled faunal distributions.