Abstract: A catalyst component for alpha olefine-polymerizing catalysts which comprise an organoaluminum compound, an external electron donor, and a solid catalyst component obtained when a solid carrier component containing magnesium has reacted with a titanium halide compound, in addition to a procedure for manufacturing the same. The catalyst component is produced by reacting a solid carrier component with a titanium halide compound with or without the presence of an internal electron donor. The solid carrier component is prepared by(a) dissolving or suspending a magnesium compound in ethanol or water,(b) adding to the solution or suspension, hydrochloric acid in a substantially stoichiometric quantity to the magnesium, to completely dissolve the same,(c) drying the magnesium solution with the aid of periodic azeotropic distillation, and(d) precipitating the solid carrier component from the thus-dried solution.