Greater Mackellar Island, also Great Mackellar Islet, is the largest of the Mackellar Islands, lying 4 kilometres (2 nmi) north of Cape Denison in the center of Commonwealth Bay, Antarctica. It was discovered and named by the Australasian Antarctic Expedition (1911–14) under Douglas Mawson. The Island is about 1100 m long, and up to 500 m wide.