In order to designate the proper source rocks for the Japanese Tertiary oil, organo-geochemical study on the Japanese oil-producing sediments and crude oils has been carried out. The geochemical approach has included organic carbon analysis, identification of various hydrocarbons, determination of CPI value and metal porphyrin content, and kerogen analysis. It is suggested that most of the rocks belonging to the Onnagawa and the Funakawa Formations of middle Miocene age can be recognized to be the proper source rock for the Japanese Tertiary oil, on the basis of comparison of those rocks with the source rock criteria presented by some workers and the specific chemical relationships such as the Ni/V porphyrin ratio, concentration of polycyclic aromatics and CPI values between crude oils and their presumed source rocks. The data of the depth-porosity curve, the geothermal gradient and the vertical evolution of organic matter constituents obtained in the Kameda oil field, Akita Prefecture lead to the conclusion that the petroleum hydrocarbon was formed by thermal degredation of organic matter near the boundary of the Kameda and the Gongenyama Formations of middle Miocene age in the time of deposition of the Kitaura Formation of late Miocene age, and the burrial depth and the temperature required for petroleum genesis in that time were about 1200-1300 m and 60-70℃ respectively.