The thermal diffusivities of 2-ethoxy-2-methylpropane (ETBE) and 2-methoxy-2-methylbutane (TAME) (mass purity > 0.990, GC) were measured by.the dynamic light scattering method. The investigated p T regions are T = (293 to 523) K and p = (4 to 10) MPa, including saturated liquid, saturated vapor, and liquid. The expanded relative uncertainty in thermal diffusivity was estimated to be less than 2.4% over the whole investigated range. The influences of temperature and pressure on thermal diffusivity were presented. The empirical correlation of thermal diffusivities for both saturated liquid/vapor and liquid were also proposed with absolute average relative deviations (AARDs) of 0.22 and 0.26% for saturated-liquid ETBE and TAME, 0.13 and 0.20% for saturated-vapor ETBE and TAME, and 0.23 and 0.69% for liquid ETBE and TAME, respectively.