A solid hydrocarbon-insoluble, alpha-olefin polymerization catalyst component with superior activity, stereospecificity and morphology characteristics, comprises the product formed by (a) complexing a magnesium alkyl composition with an organophosphoryl compound; (b) reacting the resulting stable complex with a compatible precipitation agent to form a solid component; and (c) reacting the resulting solid with a titanium (IV) compound and an electron donor compound in a suitable diluent.