The middle Pleistocene Matsugae mammalian fauna from the Matsugae limestone cave deposits in northern Kyushu, West Japan is reexamined based on the original fossil specimens and its biostratigraphical age is estimated. The Matsugae fauna includes 13 mammalian species representing 6 orders, 10 families and 12 genera that can be confirmed based on currently available fossil specimens. The taxa of the Matsugae fauna fall into four categories: the first encompasses a mammal that has been in existence since the early middle Pleistocene; the second comprises mammals that existed only during the middle middle Pleistocene; the third includes those that have specific characteristics of this age but may have a phyletic relationship to later Japanese mammals; and the fourth includes the direct ancestors of modern Japanese endemic species. The second and the third categories include several endemic taxa which are only known from this fauna. The mammalian fauna suggests an age referable to the Quaternary Mammal zone 4 (QM4), which is the middle part of the middle Pleistocene.