Gnathothlibus australiensis is a moth of the family Sphingidae. It is known from the Northern Territory and Queensland. The length of the forewings is 33–38 mm. It is similar to Gnathothlibus eras but differs in its smaller size and the complete absence of any long hair scales on the foretarsi and a clear reduction in length and thickness of long hair scales covering the foretibiae in males. It differs from Gnathothlibus vanuatuensis in smaller size and more unicolorous appearance. The head and thorax are dorsally medium brown, the abdomen is slightly lighter brown and there is a small dark median spot on the prothorax. The thorax has a ventral whitish patch immediately posterior to labial palps, the remainder is light creamy-brown. The underside of the abdomen is light pinkish-brown, with