'swift fierce dragon') is a genus of compsognathid theropod dinosaur from the Huajiying Formation from Hebei Province in China.

The holotype material consists of a pelvis, tail base and hindlimbs that had previously been part of a chimera containing three different animals.

The animal is described as being the smallest known member of Compsognathidae, being about the size of the sub-adult Scipionyx holotype specimen or approximately 0.5 meters (1.6 feet) in length.

[1] In the original description, Xunmenglong is recovered as a compsognathid in a polytomy including Compsognathus, Huaxiagnathus and Juravenator.

However, Andrea Cau (2024) recovered Xunmenglong not as a compsognathid, but instead as a basal member of Tetanurae.