Arguimus khosbajari gen.n., sp.n., assigned to the Peramuridae, is described on the basis of a single lower jaw with P2-M2, found at the locality of Khovboor (Guchin Us somon, Gobi Desert), Mongolia, in beds of presumable Aptian or Albian age. Arguimus khosbajari differs from the Upper Jurassic Peramus tenu!rostr!s in: 1) having a somewhat molarized P4 2) smaller paraconld on M2 3) absence of an entoconid on M1 and M2 4) lack of the dlastemas between the premolars, and 5) by a distinct asymmetry in lateral view of the lower premolars.