The simultaneous reduction kinetics of Cr₂O₃, MnO, FeO, and SiO₂ in the EAF slag by aluminum has been investigated at 1 793 K to understand the reduction mechanism of each oxide in the stainless steelmaking conditions. The reduction degree of MnO reached about 90% and that of FeO and Cr₂O₃ reached about 80% for 5 min. The reduction degree of SiO₂ continuously increased up to about 55% for 20 min, followed by a constant value. The reduction of each oxide by aluminum was found to be controlled by the diffusional mass transfer process in slag phase from the simple kinetic analysis. The mass transfer coefficient of each oxide was in order of ‘MnO>Cr₂O₃≅FeO>>SiO₂’ in the present system. The reduction rate constant (log K_o^MO, where MO represents Cr₂O₃, FeO, MnO, and SiO₂) linearly increases by increasing the product of diffusion coefficient and the activity of each oxide (log[D_M·a_MO]) in the slag.