Diffusion coefficients of silicon and manganese in liquid iron (carbon-saturated) were determined in temperature range between 1, 300°and 1, 600°by the method of so-called semi-infinite medium. Blank values accompanied with the measurement of diffusion in liquid state were examined and the following results were obtained : (i) Diffusion coefficients of silicon in Fe-C (saturated)-Si(1.5%) alloys can be expressed as follows : log D (cm^2sec^) = -3.62 - 0.179 × 10^4/T, activation energy Q = 8.2 kcal/g・atom. (ii) Diffusion coefficients of manganese in Fe-C(saturated)-Mn(2.5%) alloys can be expressed as follows : log D (cm^2sec^) = -3.71 - 0.127 × 10^/ T, activation energy Q = 5.8 kcal/g・atom
