Abstract: Heating experiments to simulate hydrocarbon generation have been made for two kinds of Coccolithophoridaes which belong to the same species but live in different water-temperature environments, and the mechanism of hydrocarbon generation of Coccolithophoridaes has been discussed. It shows that there are many kinds of crude-oil, hydrocarbons in Coccoljthophoridaes, and the distribution of n-alkanes and isoprenoid alkanes generated by heating is similar to that of oil-source rocks containing Coccolithophoridaes, Experiments on temperature dependence of the, generation of Coccolithophoridaes indicate that the generation of a large quantity of chloroform and the essential change in hydrocarbon composition take place at 200- 300 C. The product of this stage corresponds to the oil-source rocks containing coccolithophoridaes with an Rc range of O.35～0.55％, as is in the case of low-maturity crude oil. This study a1so discusses the isoprenoid in the products of heating experiments on coccolithophoridaes, such as phytenes and C20-, C22- Camtane. A compound considered as C22- Dimethyl-Cyclahexane has been discovered in the experiments.