P-wave velocity (Vp) and the anisotropy of lawsonite and epidote blueschists were measured up to 1.0GPa and 400°C using the ultrasonic pulse transmission technique. The slowest Vp in the direction normal to foliation is similar between lawsonite and epidote blueschists (7.0-7.2km/s at 1.0GPa and room temperature), while the fastest Vp in the direction parallel to lineation markedly differs between lawsonite blueschists (7.4-7.6km/s at 1.0GPa and room temperature) and epidote blueschist (7.9km/s at 1.0GPa and room temperature). Crystallographic orientation measurements for main constituent minerals revealed that both epidote [010] axes (fastest Vp direction in epidote single crystal) and amphibole [001] axes (fastest Vp direction in amphibole single crystal) are preferentially oriented parallel to lineation to enhance Vp anisotropy of the epidote blueschist. In contrast, lawsonite [001] axes (fastest Vp direction in lawsonite single crystal) are oriented subnormal to foliation, whereas amphibole [001] axes are oriented subparallel to lineation, so that relatively weak Vp anisotropy was observed in the lawsonite blueschist. Our experimental results, in conjunction with recent seismological observations, suggest that the Vp of the subducting oceanic crust at <50km beneath NE and SW Japan is similar to those of blueschists (9-12% lower Vp than peridotite). In contrast, the Vp in the subducting oceanic crust markedly increases at deeper than ∼50km depth beneath NE Japan, and such a slight low-velocity layer (5-8% slower Vp) at >∼50km has been observed in several subducting slabs. However, the high Vp values at >∼50km depth are difficult to be explained by blueschists. This indicates that the blueschist would be at least partially transformed to hydrous mineral-bearing eclogite at ∼50km depth in subducting oceanic crusts. © 2010 Elsevier B.V.