An oxygen stable isotope study of molluscan macrofossils from the Tithonian to the Eocene of the James Ross Island and Alexander Island areas, Antarctica, was carried out in conjunction with careful petrographic, mineralogical and geochemical analyses to assess the state of fossil preservation. The Alexander Island samples all showed evidence of alteration whilst samples from James Ross Island were variably preserved. The isotopic composition of those samples which met the textural and chemical criteria for well preserved primary skeletal carbonate material were then used to construct a record of high latitude marine water temperature variation. This record shows a marked cooling of palaeotemperatures from the late Jurassic to the Albian, a warming in recorded palaeotemperatures during the mid Cretaceous and a gradual cooling from the mid Cretaceous to the Eocene. The isotopic pattern parallels that from low latitude sites and suggests that climatic change was global and that relatively uniform latitudinal palaeotemperature gradients may have been maintained during a time of greenhouse climate. Using the James Ross Island data to calculate probable polar temperatures over the adjacent Antarctic continent shows that cold temperate or sub-polar conditions would have been established during the Albian, late Maastrichtian and Eocene.