Euchambersia is an extinct genus of therocephalian therapsids that lived during the Late Permian in what is now South Africa and China. The genus contains two species. The type species E. mirabilis was named by paleontologist Robert Broom in 1931 from a skull missing the lower jaw. A second skull, belonging to a probably immature individual, was later described. In 2022, a second species, E. liuyudongi, was named by Jun Liu and Fernando Abdala from a well-preserved skull. It is a member of the family Akidnognathidae, which historically has also been referred by as the synonymous Euchambersiidae (named after Euchambersia).

Euchambersia was a small and short-snouted therocephalian, possessing large canines as is typical of the group. However, it is notable among therocephalians for possessing ridges on its canines and a large indentation in the side of the skull. It has been proposed that these structures supported a venom delivery mechanism. If this statement turns out to be true, then it would be one of the oldest known tetrapods to have this characteristic. In 2017, the internal structure of the skull of E. mirabilis has been used as stronger evidence in favour of the hypothesis that it was venomous; other possibilities, such as the indentation supporting some sort of sensory organ, still remain plausible.

The genus Euchambersia, more specifically the type species E. mirabilis, was first described in 1931 by Robert Broom based on a distorted fossil skull that he had previously discovered in the South African farm of Vanwyksfontein, owned by a Mr. Greathead, near the town of Norvalspont. This specimen, which constitutes the holotype, is now housed in the Natural History Museum, London, under the number NHMUK R5696. Describing the taxon as "the most remarkable therocephalian ever discovered", Broom named it after the eminent publisher and evolutionary thinker Robert Chambers, whose Vestiges of the Natural History of Creation was considered by Broom to be "a very remarkable work" though "sneered at by many". In 1966, a second, smaller skull of the same species, was discovered at the farm of Waschbank, located about 8 km (5.0 mi) from the type locality. It was first figured in 1977 by James Kitching, although he provided no description. This specimen is now catalogued as BP/1/4009 by the Evolutionary Studies Institute of the University of the Witwatersrand, where it is stored. The two known skulls of E. mirabilis, both lacking their lower jaws, originated from the same general layer of rock, in the upper Cistecephalus Assemblage Zone of the Beaufort Group within the Karoo Supergroup. The Cistecephalus AZ has been dated to the Wuchiapingian stage of the Late Permian, between 256.2 and 255.2 million years old.

In 2022, Jun Liu and Fernando Abdala described a second species, E. liuyudongi, based on a well-preserved skull with an associated lower jaw, catalogued as IVPP V 31137 in the collections of the Institute of Vertebrate Paleontology and Paleoanthropology. Few postcranial remains, including six vertebrae and some rib fragments, also come from this specimen, but they are not described by the two authors. The specific epithet is named in honor of Liu Yu-Dong, the technician who discovered the holotype specimen in 2020. This species originated from the Naobaogou Formation of Inner Mongolia, which is dated more broadly to the Lopingian epoch (which contains the Wuchiapingian). The formation is divided into three members based on cycles of sedimentation, numbere as members I, II, and III from oldest to youngest; E. liuyudongi originates from member I. Liu and colleagues had previously described a number of other new species from the middle portion of the Naobaogou Formation, which were among the 80 specimens that had been excavated from at least three field seasons after 2009.

E. mirabilis was small and short-snouted (the snout being about half of the skull length) for a therocephalian, with the type skull having a reconstructed length of approximately 11.6 cm (4.6 in), accounting for crushing and deformation in the fossil. The second known skull belonged to a smaller individual, with a length of 8 cm (3.1 in); it was probably immature, judging by the lack of fusion in the skull. The type skull of E. liuyudongi measures 7 cm (2.8 in) in length and has a shorter snout (less than 40% of the skull length).

According to the initial description, the eye socket of E. mirabilis was rather small. The branches of the postorbital and jugal that usually surround the back and bottom of the eye socket in therocephalians appear to be either very reduced or absent entirely. Meanwhile, the top of the eye socket is formed by the prefrontal, and the frontal is also small. The skull does not bear a pineal foramen. Like Whaitsia, the pterygoid and palatine of the palate are not separated from the transpalatine, further to the side of the jaw, by any sort of opening. E. liuyudongi differs from E. mirabilis in several details of these bones: the frontal bone separates the prefrontal from contacting the postorbital, and the postorbital fenestrae at the back of the skull are slit-like instead of rounded. Additionally, the epipterygoid and prootic of the braincase are disconnected in E. liuyudongi.

Although the skulls of E. mirabilis are incompletely preserved, CT scanning suggests that each premaxilla held five incisors, with the sockets becoming progressively larger from the first to the fifth incisor. Like other theriodonts, the crowns of the incisors are conical; they also lack serrations, unlike gorgonopsians and scylacosaurian therocephalians. The interior edge of the incisors seems to be slightly concave, and the back edge appears to have a ridge. The smaller specimen has a displaced incisor preserved within its nasal cavity; it is more strongly recurved and has wear marks on its top edge, suggesting that it is probably a lower incisor. Its fourth incisor also has a replacement tooth growing behind it, accompanied by resorption of the root.

The type specimen of E. mirabilis preserves the right canine. Like other therocephalians, its canine was very large, resulting in a specialized predatory lifestyle that incorporates a sabertooth bite into prey killing. It is round in cross-section, and bears a prominent ridge on the side of its front surface. Immediately beside this ridge is a shallow depression that becomes wider near the top of the tooth, which is probably the same structure as the groove interpreted by some authors. Unlike E. mirabilis, however, the canines of E. liuyudongi had neither ridges nor grooves. Theriodonts usually replace their teeth in an alternating (or distichial) pattern, such that the canine tooth is always functional; both skulls of E. mirabilis show no sign of any replacement canines developing, suggesting that it was reliant on having both canines present and functional simultaneously.