The measurements of the elastic wave velocity of lower crustal rocks may provide valuable information on the composition and physical properties of the lower crust. The samples from old granulite terrane cropped out on the earth surface are often taken as the representatives of the lower crust, because of the difficulty of directly sampling the lower crust. The obtained results, however, are often in compatible with the actual conditions, as the old granulite terrane had experienced long period of multi-stage deformation and metamorphic processes. In Contrast, the lower crustal xenoliths brought up by Cenozoic basalts onto the surface may provide us with direct information of the lower crust. The measurements of density and elastic wave velocity of lower crustal xenoliths from Hanuoba basalts, Hebei Province, China under high temperature and pressure conditions are presented in this paper. The study shows that the lower crust of the area consists of various types of granulite facies rocks. Their density and velocity are different significantly from each others. The measured velocity of lower crustal xenoliths, therefore, can not be directly compared with the velocity structures of the lower crust obtained from deep seismic sounding, without temperature and pressure corrections. An in-situ velocity of lower crust of 6. 13 - 6. 90 km/s is obtained from this study, which is comparable well to the seismic data from the studied area. In addition, the origin of the low velocity layer is discussed as well.