The Collett's Snake - also known as the Down's Tiger Snake, Collett's Black Snake or Colletts Cobra - is a venomous snake native to Australia. Although the Collett's Snake is not as venomous as other Australian snakes, it is capable of delivering a fatal bite, ranking nineteenth in the world's most venomous snakes.

The most colourful member of the black snake genus Pseudechis, it has dark brown to black upperparts, with pink or cream banding and sides, and pale yellow to orange underparts. The irregular bands are usually cross-shaped and are generally an orange-red colour. The Collett's underbelly is normally the same colour as its bands, but may have varied discolourisations or discoloured patches. Juveniles are usually the same colour as adults but generally have brighter shades and contrast more. It is similar in physical structure (but not appearance) to the Red-Bellied Black Snake.

Males can reach up to 2.6 metres in length, while females can reach up to 2.1 metres. They are usually 30 centimetres in length at birth.

Previously thought to be only moderately venomous to people, Collett's snake is now known to have been responsible for severe envenomation, with cases proceeding to rhabdomyolysis and acute renal failure. Toxicity and symptoms of the venom resemble that of the mulga snake (P. australis). Early symptoms include nausea, vomiting, abdominal pain, diarrhoea and headache, an anticoagulant coagulopathy, with risk of rhabdomyolysis and acute renal failure within 24 hours if fluid replacement and black snake antivenom are not given. Despite the danger, its attractive markings have led it to being a popular snake in captivity.

The venom produced by the Collett's Snake is similar to the Papuan Black Snake's and Mulga Snake's venom. The venom is cytotoxic and has haemolytic activity. Neurotoxins may also be found in its venom as well. Collett's produce around about 30 milligrams of venom in one strike. Black Snake or Tiger Snake anti-venom can be administered.

The Collett's main diet consists of frogs and plague rats. Being diurnal they hunt during the day and feed by injecting their fangs into their prey and pumping their cytotoxic venom into them. Cannibalism is also known to occur in Collett's Snakes. When provoked, Collett's will produce a loud hissing noise and may produce a series of warning strikes. Although they are placid snakes, they will bite if under threat.

Mating occurs from early August to late October, where hatchlings emerge 2–3 months later. It is oviparous, and lays clutches of up to 13 eggs. Reproduction in captivity is known to be highly successful.