Eucalyptus nicholii, commonly known as the narrow-leaved black peppermint or willow peppermint, is a Eucalyptus tree native to New South Wales. The tree is small to medium-sized with rough bark, persistent to small branches. The bark is fibrous, coarsely fissured longitudinally, yellowish-brown to grey-brown with red-brown under-layers becoming smooth and grey on outer branches and shedding in short ribbons. It is a long lived tree that grows to 15 meters.