A continuous process for preparing a metallic soap by a double decomposition process is disclosed, in which an aqueous solution of an alkali soap and an inorganic metal salt are separately fed directly on the surface of the rotating impeller of a mixer to instantaneously mix them together and the resulting metallic soap aqueous slurry is discharged out from the mixer without delay. Metallic soaps free from contamination with unreacted starting materials or by-products can be continuously obtained using small-sized reactor vessels with a reduced energy.