Two types of different realms within Japanese Upper Triassicfaunas are recognizable, their ages are discussed. The Kochgatani Fauna isthe representative of the Arcto-Pacific realm, its early group is revised to Car-nian to Lower Norian in age while its late group is regarded to middle-upperNorian to Rhaetian. The megalodont assemblage and the "St. Cassian" faunaof Japan are both belonging to the Tethyan realm, they may correspond to therelevant faunas of late Carnian or early Norian age of south China. The resultis significanily for further studying the Chinese nonmarine Upper Triassic se-quence.