The temperature distribution across the transition zone has been determined on the high-pressure phase equilibria in the system Mg2SiO4-Fe2SiO4 recently determined by Katsura and Ito [1988> and Ito and Takahashi [1988>. The temperature at the base of the transition zone (655 km depth) is estimated to be about 1600 ¿C, assuming that the spinel dissociation is responsible for the sharp seismic discontinuity implied by study of reflected waves. This estimation would be little modified for the chemically stratified mantle models, since the lower mantle is characterized by the stability of perovskite. The temperatures in the region from 350 km to 655 km depth are calculated for a peridotitic mantle model, assuming an adiabatic temperature gradient. The &agr;-&bgr; and &bgr;-&ggr; transformations in (Mg,Fe)2SiO4 make the temperature profile steep in the depth regions of 390--415 km and 500--530 km, respectively. The temperature would increase from about 1400 ¿C to 1600 ¿C over the depths interval 350 between 655 km. ¿ American Geophysical Union 1989