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.

The island forms part of the Mackellar Islands Important Bird Area (IBA), identified as such by BirdLife International because it supports large breeding colonies of Adélie penguins.

• List of Antarctic and Subantarctic islands

• Sketch map
•  This article incorporates public domain material from "Greater Mackellar Island". Geographic Names Information System. United States Geological Survey.