This article researches the Japanese land system before modern times, especially in the Heian period. The relation between possession and title is widely different from that in modern law where the proprietary right is conceptual and absolute. In the Heian period, the right to land was expressed by many different forms. Possession（chigyo）was justified by various titles called ri, which included documents issued by authority, assurance, lineage, cultivation, precedent, long-term possession, and so forth. These titles were claimed by the litigant parties and recognized by judges in courts. Previous studies have argued that in Japanese land law before modern times, documents issued by the authorities represented a definite right to the land. But the diversity of titles in the Heian period is a remarkable characteristic common to medieval law.