Phrynoidis juxtaspera is one of the two river toads. It can get as big as a small rabbit (males up to 120 mm, females 215 mm snout-vent length). The warts have thoroughly keratinized apices. The warts behind the eyes (parotic glands) are thick and long (smaller and a more broken up in Phrynoidis aspera). 

The toads secrete large amounts of highly toxic, milky poison from their warts when molested (photo). Not only skin secretions of adults but also eggs and tadpoles are poisonous. Adult males 70–120 mm snout-vent length, females 95–215 mm. We observed a huge specimen at Tawau Hills NP (s. photo) quietly sitting in a picknick area and feasting on large Camponotus ants that passed by. 

Large specimens are hunted for food in some areas: the toad must be carefully skinned, washed before cooking to remove the poison.

The toad has extensive webbing between toes and is a good swimmer; strong legs make it a good jumper as well.

The tadpoles are small, dark brown to black, and live in stream and have an oral disc in the form of a sicher, with which they can cling to rocks.