An investigation of materials of Japanese oil paintings in the late nineteenth century has been carried out to identify the physical origin of the materials. In previous examinations with X-ray microanalyzer and X-ray diffractometer, forty-three grounds which seemed to be commercially-prepared priming were subjected to examination. It was found that the grounds were classified into 1) calcium carbonate type, 2) lead white type, and 3) others, according to their elements and structures. In this paper, small fossil-like substances about 10mum in diameter observed in most of the calcium carbonate type grounds are examined. Optical microscopical examination has revealed that the fossil-like substances were calcareous nannofossils. From measurements of percentages of species of calcareous nannofossils, it appears that the calcium carbonate was chalk of the Champanian period of the late Cretaceous era. Since geologically there was no chalk in Japan during this period, the result has suggested that chalk used on canvas might have been brought from Western Europe to Japan in the late nineteenth century.