Lesser Mackellar Island is a small island immediately northeast of Greater Mackellar Island in the Mackellar Islands of Antarctica, lying 4 kilometres (2 nmi) north of Cape Denison in the center of Commonwealth Bay. It was discovered and named by the Australasian Antarctic Expedition (1911–14) under Douglas Mawson. The name is indicative of the size of the feature in relation to Greater Mackellar Island.