Underwoodisaurus milii is a species of lizard. It is commonly known as the thick-tailed gecko or barking gecko, and has a sharp, barking defensive call, as well as a distinctive tail which is flanged at the base. It is reddish-brown with bands of white and yellow spots, and paler underbelly, and grows to be about 95 mm long. It is native to Australia. It is slightly more cold-tolerant than many other Australian geckos, and ranges through a variety of habitats in southern Australia. It is nocturnal and terrestrial, and it prefers to prey on insects.