Abstract: The ctenodactyloids from the Eocene of Mongol include 10 species representing 4 genera (Gobiomys neimongolensis, G. exiguus sp. nov., G. cf. G. xiguus, G. asiaticus sp. nov., Gobiomys? spp., Advenimus cf. A. bohlini, A. cf. A. burkei, Yuomys sp. and Protataromys sp.). The new genus, Gobiomys, is erected based on the species, neimongolensis, which has previously been referred to Mergenomys. The main characters of Gobiomys are: incisive foramen large; P3 present; cheek teeth lower crowned, with distinct but not swollen main cusps and broad sinuses; non-molariform; upper molars wider than long, with rather developed metaloph; Ml and M2 with entoloph; on lower molars metaconid and entoconid inclining forwards and ectolophid and hypoconulid slightly buccally located. The main features of G. eyguus small size, zygomatic process of maxillary anterior to P3, absence of lingual part of posterior arm of protoconid, ann of entoconid and anterior cingulum on lower molars. In G. asiaticus the posterior edge of the zygomatic process of maxillary is buccal to P3; the molars have more developed lophs; the upper molars are relatively wide and have weaker metaconule; and the lower molars have more developed arm of entoconid and anterior cingulum. The new family, Gobiomyidae, includes Gobiomys, Mergenomys, Youngomys and Ctenodactyloidea gen. nov. from Kazakhstan [see Wang et al., (MS)]. In the family the lower jaw lacks upper crest of masseteric fossa. The cheek teeth are brachydont and more bunodont than lophodont. P3 is usually present. P4/p4 are nonmolariform. On the upper molars the protoconule is absent, the metaloph extends towards protocone or absent and the metaconule is usually well-developed. The p4 has no metalophid. On lower molars the posterior arm of protoconid extends rather posteriorly and die am of entoconid is weak or absent. The ectolophid is near centrally located and has no mesoconid. The Gobiomyidae represent the sister group to the Ctenodactylidae.