Amphitherium is an extinct genus of stem cladotherian mammal that lived during the Middle Jurassic of England.

A recent phylogenetic study found it to be the sister taxon of Palaeoxonodon.

Although he thought the jaws were mammalian, the anatomist Georges Cuvier misidentified them as being from a marsupial mammal, Didelphis.

It came from the Stonesfield Slate of Oxfordshire, England, and Buckland described it in 1824 as "not less extraordinary" than the dinosaur,[4] but it was the larger fossil reptile that captured public imagination.

Additional remains were recovered in the late 20th century from the Kirtlington Quarry and Watton Cliff, both part of the Forest Marble Formation Other early mammal discoveries included Amphilestes, Phascolotherium, and the mammal relative, Stereognathus.