Abstract: The Houldjin Formation was discovered and named by the Third Asiatic Expedition in 1922. Its geological age was first considered as Miocene or later, then varied from Oligocene to Late Eocene because of scarcity of mammalian fossils found in that formation. Since 1985, some additional mammalian fossils have been found. These discoveries have throw more light on its age determination. The micromammalian fossils have already been reported. The large mamma鄄 lian fossils, except paraceratherines, are described here.