Abstract: A catalyst component for alpha olefine-polymerizing catalysts which comprise an organo-aluminum 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 a natural or synthetic mineral containing magnesium and aluminum in hydrochloric acid,(b) evaporating the solution until dry,(c) calcinating the obtained salt mixture from the evaporated solution by heating the same at a temperature of about 130.degree.-150.degree. C.