The upper mantle geotherm and rheology for Mingxi, Fujian Province, has been constructed through a detailed study of mantle xenoliths collected from this area. The constructed geotherm is higher than the oceanic geotherm and slightly lower than those for eastern China and southeastern Australia. The crust-mantle boundary as derived from this geotherm is located at a depth of about 38 km, but spinel lherzolite was found at a depth of 32 km, indicating the under-plating of upper mantle materials. Moreover, the equilibrium temperatures of some spinel lherzo-lites are within the same range as those of some garnet lherzolites. It seems to indicate that there is no distinct boundary between spinel Iherzolites and garnet Iherzolites, and that there should be a transition zone 5~10 km thick between the two, instead. The deformation features of the xenoliths have revealed that a strong deformation event occurred within the upper mantle of this area. It might be related to upper mantle diapirism. As a result, some zones characterized by a high strain rate and a low viscosity occurred at a depth of about 65 km, which resemble the upper mantle shear zones proposed by Downes.