Olefin polymerization catalysts for producing polyolefin resins which can dispense with a melt-kneading step necessitating great energy or a substitute addition step therefor and to which small amounts of antioxidants have been effectively added; and a process for the production of the catalysts. Specifically, a catalyst for olefin polymerization characterized by being prepared by conucting prepolymerization in the presence of I a solid catalyst for olefin polymerization having a mean particle diameter of 10 to 200µ m, II an antioxidant for resins, and III an olefin;and a catalyst for olefin polymerization characterized by containing IV an organoaluminum compound in addition to the components I to III.