Liaoningosaurus (meaning "Liaoning lizard") is an unusual genus of basal ankylosaurid dinosaur from the Liaoning Province, China that lived during the Early Cretaceous (late Barremian to early Aptian stages, ~125.4 to 118.9 Ma) in what is now the Yixian and Jiufotang Formation. The type and only species, Liaoningosaurus paradoxus, is known from more than 20 specimens, represented by juvenile individuals. It was named in 2001 by Xu, Wang and You.

L. paradoxus was unusual among ornithischian dinosaurs in that it is speculated to have hunted or scavenged, with preserved gut contents showing that it may have eaten fish. Additionally, some features of its skeleton may suggest that it was partially aquatic. However, not all paleontologists agree with this interpretation. It is the oldest ankylosaurid to have had a tail club and had a wide paleogeographic and stratigraphic distribution in western Liaoning. Both Liaoningosaurus and Chuanqilong show various similarities with one another, with the latter being suggested to be a later growth stage.

The remains of a juvenile ankylosaur were collected by members of the Western Liaoning expedition team of the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) from the Baicaigou locality in the Liaoning Province, China. It was recovered from the Dawangzhangzi Bed of the Yixian Formation, which dates to the late Barremian to early Aptian stages of the Early Cretaceous period. The specimen was named and described in 2001 by Xing Xu, Xiao-Lin Wang and Hai-Lu You. The generic name, Liaoningosaurus, is derived from the Liaoning Province and the Greek word "sauros" (lizard). The specific name is derived from the Latin word "paradoxus", in reference to a suite of highly unusual traits for an ankylosaur. The type specimen, IVPP V12560, consists of a nearly complete, articulated skeleton measuring approximately 34 centimetres (1 ft 1 in) in length that was preserved with the ventral surface exposed on a slab.

In 2016, a nearly complete skeleton of Liaoningosaurus was described by Ji Qiang, Wu Xiaochun, Cheng Yennien, Ten Fangfang, Wang Xuri and Ji Yannan. The specimen, XHPM-1206, was collected from the Jianshangou Bed of the Yixian Formation, about 160 km west from the holotype locality. The authors noted that the specimen was slightly larger than the holotype and shows features that were either previously unknown or not accurately described in the holotype such as the humerus being almost as long as the femur or tibia and the presence of five digits rather than four on the manus (hand). It is currently housed at the Xinghai Museum of Paleontology. Arbour & Currie (2015) referred two specimens; CYGYB 208, a nearly complete skeleton that is preserved on a slab with the dorsal (upper side) surface exposed; and CYGYB 237, a nearly complete skeleton that is preserved on a slab with the ventral (underside) surface exposed.

In 2022, Chang-Fu Zhou, Qing Liu, Xinyue Wang and Honggang Zhang described a nearly complete, associated skeleton (PMOL-AD00105) of Liaoningosaurus from the Jiufotang Formation of the Liaoning Province, China. The authors considered that the presence of Liaoningosaurus in the Jiufotang Formation supports the possibility of a wide paleogeographic and stratigraphic distribution in western Liaoning. A Canadian Society of Vertebrate Palaeontology abstract book that was published in 2019 mentioned that about 20 specimens had been collected from four different localities of the Yixian Formation, and one locality from the nearby Jiufotang Formation.

The type specimen of Liaoningosaurus has an estimated length of about 34 centimetres (1 ft 1 in). It has a skull-sacral length of 17.2 centimetres (6.77 inches), while a second specimen, XHPM-1206, has a skull-sacral length of 19.3 centimetres (7.6 in). The largest specimen, GPMA-12-045, has a total body length of less than 45 centimetres (1 ft 5 in) and a skull-sacral length of 21 centimetres (8 in), and the smallest specimen, NGMC-98-003, has a preserved length of 22 centimetres (8.66 in) with a skull-sacral length of about 16 centimetres (6.299 in). A juvenile skeleton from the Jiufotang Formation has a total estimated body length of 30 centimetres (11.8 in).

The skull of Liaoningosaurus, like Chuanqilong, may have had an antorbital fossa or fenestra, as implied by a posteriorly excavated maxilla. An external mandibular fenestra is also present. The dentary bone has a straight ventral margin and has a stout appearance. On each premaxilla, slender teeth with few denticles are present. Premaxillary teeth are also seen in some basal nodosaurids and Gargoyleosaurus. There are only approximately 10 maxillary teeth, which has been suggested to be due to its juvenile status. However, the ontogenetic variation in the number of teeth is less than 10 among all known ankylosaurs. The tooth crowns are similar to those of Crichtonsaurus (or Crichtonpelta). The teeth have a shelf-like cingulum at their bases, and a palmate crown which bears vertical flutes that coincide with the notches between marginal cusps.

Both the scapula and humerus are slender in appearance. The scapula has a narrow scapular base and a scapular spine that may have been directed towards the glenoid. The humerus has a deltopectoral crest that extends less than half the length of the shaft. The radial condyle of the humerus is poorly developed, while the olecranon process of the ulna is moderately developed. The manus is short. Xu et al. (2001) originally recorded the manual phalangeal formula as 2-3-3-2. However, Ji et al. (2016) noted the presence of five digits (fingers) rather than four in one specimen of Liaoningosaurus. The femur has an indistinct femoral head and a crest-shaped trochanter present on the mid-length of the shaft. The tibia is as long as the femur. The pes (foot) is about 230% as long as the manus. Metatarsals II–IV are elongate, while metatarsals I and V are splint-like. The pedal phalangeal formula is 0-3-4-5-0. Both the pedal and manual unguals are triangular in dorsal view, a condition also seen in Dyoplosaurus.