Characteristics of geometry of slabs and the intraslab stress filed in the Nankai subduction zone, Japan, were analyzed based on highly accurate hypocentral data and focal mechanism solutions. The results suggest that the shallow seismic zones of the Philippine Sea slab subduct with dip angels between 10 and 22 degrees beneath the Shikoku area and the Kii peninsula. The dip angle of the seismic zone changes from 11 to 40 degrees beneath Kyushu. Two types of seismogenic stress field exist within the slabs of the Philippine Sea plate in the Nankai Trough. The stress field of down-dip compression type can be seen in the slab beneath the region from the western part of Shikoku to the Kii peninsula, where the horizontal component of regional compression stress is nearly in the NWN direction. On the other hand, the stress field of down-dip extension type within the slab is dominant in the region from the western part of Shikoku to Kyushu, where the direction of horizontal compressive stress is near the WNW. Characteristics of geometry of slabs and the intraslab stress filed are related to the slab age of the subduciton zone. The young slab of the oceanic Philippine Sea plate subducts with shallow angle beneath the Eurasian plate in the Shikoku region and the Kii peninsula. The subduction has encountered strong resistance there, resulting in a down-dip compression stress field. The down-dip extension stress field may be related to the older slab of the Philippine Sea plate which subducts beneath the Kyushu region with a steeper dip angle. Characteristics of geometry of slabs and the intraslab stress filed in the Nankai subduction zone, Japan, were analyzed based on highly accurate hypocentral data and focal mechanism solutions. The results suggest that the shallow seismic zones of the Philippine Sea slab subduct with dip angels between 10 and 22 degrees beneath the Shikoku area and the Kii peninsula. The dip angle of the seismic zone changes from 11 to 40 degrees beneath Kyushu. Two types of seismogenic stress field exist within the slabs of the Philippine Sea plate in the Nankai Trough. The stress field of down-dip compression type can be seen in the slab beneath the region from the western part of Shikoku to the Kii peninsula, where the horizontal component of regional compression stress is nearly in the NWN direction. On the other hand, the stress field of down-dip extension type within the slab is dominant in the region from the western part of Shikoku to Kyushu, where the direction of horizontal compressive stress is near the WNW. Characteristics of geometry of slabs and the intraslab stress filed are related to the slab age of the subduciton zone. The young slab of the oceanic Philippine Sea plate subducts with shallow angle beneath the Eurasian plate in the Shikoku region and the Kii The subduction has encountered strong resistance there, resulting in a down-dip compression stress field. The down-dip extension stress field may be related to the older slab of the Philippine Sea plate which subducts beneath the Kyushu region with a steeper dip angle .