A method for producing a homopolymer or copolymer of an .alpha.-olefin is disclosed, wherein a specific catalyst is used, said catalyst comprising a solid catalyst component obtained by contacting, in the presence of a chlorinated hydrocarbon solvent, a titanium compound and an aromatic carboxylic ester with a solid component obtained by reacting a hydrocarbon solvent-soluble organomagnesium compound having an alkoxy group with a specified chlorosilane compound having an Si--H bond; an organoaluminum compound; and an alkoxysilane compound. By the method of the present invention, an .alpha.-olefin homopolymer or copolymer exhibiting high bulk density and stereoregularity can be efficiently produced under even such polymerization reaction conditions, that the polymerization temperature is high and the polymerization time is long.