Ultramafic xenoliths are found in Kishyuku Lava, Fukue-jima, Southwest Japan. These include spinel lherzolite, harzburgite, dunite as well as pyroxenite. The compositions of the constituent minerals of the peridotite xenoliths are in the range of the upper mantle peridotites. Low TiO2 (< 0.05 wt%) and high Cr/(Cr + Al) ratio (< 0.5) in spinel, together with high Fo up to 92, indicate that the xenoliths are derived from depleted part of the mantle. The combination of clinopyroxene and olivine geothermobarometry (Köhler and Brey 1990) and clinopyroxene and orthopyroxene geothermometry (Brey and Köhler 1990) applied to the xenoliths yields an extremely high geotherm of 1070 oC at 1.0 GPa up to 1200 oC at 2.2 GPa. The stability of spinel lherzolites at such high pressures is consistent with the high Cr/(Cr + Al) in spinel. Existence of such depleted upper mantle is compatible with the model of asthenospheric injection during the rifting of the Northeast China and the Japan Sea (Tatsumi and Kimura 1991). The high geotherm is the thermal perturbation due to the injection of the hot asthenosphere and/or post-rifting uprise of mantle diapirs since 11 Ma.