A deoxidizing agent for molten steel, which is an alloy of aluminum and at least 2 mole %, based on the aluminum, of an element of Group IIIa of the periodic table. In steel which has been deoxidized with this deoxidizer, an oxide inclusion based on the deoxidizer is not dendritic but spherical, and does not cause defects to steel products. Misch metal is especially preferred as the Group IIIa metal.