The reef-building scleractinian coral Oulastrea crispata (Lamarck) has a conspicuous black skeleton. Skeletal pigments of O. crispata from 10 sites in Japan were measured quantitatively to compare geographic variation in skeletal color of the species. The level of pigment concentration varied from place to place, but showed no consistent pattern with the geographic distribution. Cross transplantation experiment between two of the sites showed that the skeletal color is changeable in both directions rather than being a genetically fixed trait at each site. Although environmental factor(s) controlling skeletal pigmentation has not been specified, it is assumed that light and sea water temperature are not involved in skeletal pigmentation.