Multiple-filter analysis is applied to surface waves with their paths almost entirely inside the Philippine Sea plate. The resulting dispersion data are used to study the crustal and upper mantle structures of the plate. Effort is made to examine the intraplate structural variations. Part of the Philippine Sea plate appears to have a thin plate thickness of about 30 km and is overlying a very low velocity mantle. Lateral structural variations in the plate are indicated by the dispersion data. The plate can be divided into several elongated regions, all of which are parallel to the eastern plate boundary and each having a rather distinct crustal and upper mantle structure. The active marginal basin region, located immediately to the west of the Mariana trench, probably represents an area of lithospheric generation. This is supported by the very low shear wave velocity, high heat flow, and magmatism. The Kyushu-Palau ridge along the central portion of the plate seems to have a thicker lithosphere, in contrast to its two flank regions, the Philippine basin and the Parece Vela basin.