Heat transfer coefficient between bubble phase and emulsion phase studied in the system of sand and γ-alumina particles fluidized by dry air. Gas velocity ratio to minimum fluidization velocity of the particles （U₀/U_mf） were taken in the range of 1.05 to 8.6, and the settled height of the particle to diameter of the bed(L₀/D_t) was fixed to 2, and the solid bed was heated to about 850 ℃. And heat transfer coefficients were measured by a steady state method analyzing the data of the temperature differences between bubble phase and emulsion phase occupying a high sensibility thermocouple probe. It was found that there is a linear correlation between U_mf/D_b and H_b, here D_b and H_b indicate mean gas bubble diameter of the bed and mean over all internal heat transfer coefficient of bubble phase respectively, and that H_b are most available as a design data of the fluidized bed.