The temperature requirement for growth and the upper survival temperatures (USTs) of 15 Antarctic red algal species collected on King George Island (South Shetland Islands) and Signy Island (South Orkney Islands) were determined. Two groups with different temperature requirements were identified. 1) A “eurythermal” group includes Rhodymenia subantarctica, Phyllophora ahnfeltioides, Gymnogongrus antarcticus, and Rhodochorton purpureum, growing between 0° and 10°C with optimum values at (0°) 5°(l0°)C. The USTs of these species and of Porphyra endiviifolium, Delesseria lancifolia, and Bangia atropurpurea were between 22° and 16°C. These species survived temperatures in a similar range as most endemic Arctic or Arctic/cold-temperate species but exhibited a lower temperature demand for growth, suggesting an earlier contact with low temperatures than Arctic species. 2) A stenothermal group includes Pantoneura plocamioides, Myriogramme mangini, Ballia callitricha, Phyllophora antarctica, Gigartina skottsbergii, Georgiella confluens, and Plocamium cartilagineum growing at 0° or ≤5°C with optimum values at 0° or 5°C. The USTs of these species and of Phycodrys austrogeorgica were between 14° and 7°C. The species of this group must have had an even earlier contact with the Antarctic cold-water environment than species of the “eurythermal” group. Gigartina skottsbergii, Georgiella confluens, Plocamium cartilagineum, and Pantoneura plocamioides were probably exposed longer to low temperatures than the other species of this group or Antarctic green and brown algae because they show the lowest temperature requirements so far determined in seaweeds. The results are discussed in the context of present local temperature regimes at the localities where the isolates were collected. Moreover, an attempt was made to explain the geographic distribution of individual species by the temperature requirements determined in this study. Only a few of the distribution limits are determined by temperature growth and/or survival characteristics. In many species (Rhodymenia subantarctica, Ballia callitricha, Gigartina skottsbergii, Bangia atropurpurea, Rhodochorton purpureum, and Plocamium cartilagineum), the development of temperature ecotypes is evident.