PURPOSE: To remove efficiently impurities from molten Al or Al alloy refined by gaseous chlorine and to clean the molten metal by filtering the molten metal by pulverous sodium chloride or potassium chloride as a filter aid.

CONSTITUTION: The pulverous sodium chloride and/or potassium chloride is added at about 0.005W0.1wt% as the filter aid to the molten Al or Al alloy refined by gaseous chlorine and an inert gas is blown thereto to stir the molten metal and to disperse uniformly said sodium chloride and/or potassium chloride. The grain size of the sodium chloride, etc. is properly selected according to the pore size of a filter consisting of a porous refractory material, etc. The molten metal is preferably filtered after the filter is precoated by circulating the molten metal dispersed with the above-mentioned filter aid circulated in the initial stage of filtration. The fine impurities in the molten metal are thus effectively removed and the decrease in cleanliness is hardly obviated even if the slight chlorides mentioned above enter the molten metal subjected to the filtration.