The type species is Xixianykus zhangi described in 2010 by Xu Xing. The genus name refers to Xixia County and to the Greek word for claw ("nyx"). The latter is a common element used in names for Alvarezsaurids. The species name is in honor of Zhang Xinglao.
The fossil, holotype XMDFEC V0011, was found in the Majiacun Formation in Henan Province, China. The fossil consists of a partial skeleton, without the skull. Parts of the hind legs, pelvis and spine has also been recovered.