Thermal diffusivity of MgSiO3 perovskite has been measured in the temperature range of 160 K to 340 K using a sample synthesized in a uniaxial split-sphere high-pressure apparatus. At 300 K the thermal diffusivity of perovskite is 1.72¿10-6 m2s-1, from which the thermal conductivity is evaluated to be 5.1 Wm-1K-1. Our model calculation shows that lattice thermal conductivity of the perovskite increases by a factor of 4 with depth throughout the lower mantle and reaches to 12 Wm-1K-1 in the vicinity of the mantle-core boundary. The D' layer might not be a thermal boundary layer insulating the high core-temperature, if this layer mainly consists of the perovskite. ¿American Geophysical Union 1991