Upper Triassic limestone within the Sambosan accretionary complex in Japan contains reefal facies that accumulated on a mid-oceanic seamount in the Panthalassa Ocean. Such limestone is found at the Inaba Cave locality along the Shimanto River, central Shikoku. The reefal limestone occupies part of a bioclast-rich limestone that occurs as an allochthonous tectonic slab. The reefal limestone is characterized by sponge-algal rudstone-floatstone and coral bafflestone rich in Retiophyllia. Megalodonts floatstone also occurs in association with the reefal facies. Although the lateral continuity and exact relationship between the Megalodonts floatstone and the reefal facies remain uncertain, this is the first report in which this unique facies association has been described in the Sambosan accretionary complex.