Characteristics of organic matter content, hydrocarbon generation and expulsion of carbonate rocks are discussed by analysis of organic carbon and pyrolysis. There is a strong inhomogeneity in distribution of organic matter in carbonate rocks. The organic matter abundance is higher in stylolites, carbonate varves or marls, while it is the lowest in matrixes (purer carbonate rocks around stylolites). Because of stable thickness and broad area, marls and carbonate varves may become good source rocks. At the same depth, stylolites, carbonate varves and matrixes generate and expel hydrocarbons almost at the same time. Expulsion efficiency of carbonate varve is the highest; that of matrixes is the lowest and that of stylolites is between marl’s or carbonate varve’s and matrix’ s. Characteristics of organic matter content, hydrocarbon generation and expulsion of carbonate rocks are discussed by analysis of organic carbon and pyrolysis. There is a strong inhomogeneity in distribution of organic matter in carbonate rocks. The organic matter abundance is higher in stylolites, carbonate varves or marls , while it is the lowest in matrixes (purer carbonate rocks around stylolites). Because of stable thickness and broad area, marls and carbonate varves may become good source rocks. At the same depth, stylolites, carbonate varves and matrixes generate and expel hydrocarbons almost at the same time. Expulsion efficiency of carbonate varve is the highest; that of matrixes is the lowest and that of stylolites is between marl’s or carbonate varve’s and matrix ’s.