This paper describes Upper Triassic limestone clasts of the polymictic limestone conglomerate (Imogadaira Limestone) of the Mino Belt in the Nanjo Mountains, Fukui Prefecture, central Japan. The Imogadaira Limestone occurs as an isolated block in the Middle Jurassic mélange unit in the upper reaches of the Imogadaira River, Nanjo Mountains. The formation exhibits a prevailing conglomerate fabric, characterized by dense packing of limestone clasts within a sparse matrix. The Imogadaira Limestone has a polymictic clast association, dominated by Permian limestones with lime mudstone and limestone clasts containing thin-shelled bivalves. Neither terrigenous clastic grains nor rock fragments occur in the Imogadaira Limestone. Late Triassic conodonts and Late Triassic and Early Jurassic radiolarians were extracted from whole-rock samples of the Imogadaira Limestone. Further examination revealed that the Late Triassic conodonts and radiolarians occurred within limestone clasts containing thin-shelled bivalves.