Underwoodisaurus milii is a species of gecko, a lizard in the family Carphodactylidae. The species is commonly known as the thick-tailed or barking gecko, referring to its distinctive plump tail and sharp, barking defensive call. The genus is also often called thick-tailed geckos as a group, along with the species Uvidicolus sphyrurus.
U. milii is reddish-brown with bands of white and yellow spots, and a paler underbelly. It usually grows to a total length (including tail) of 120–140 mm (4.7–5.5 in). The original tail is black with several pale bands, however the regenerated tail has little pattern.