Process for the preparation of a catalytic composition for the polymerization of olefins. At least partial electrochemical oxidation of aluminum in a solvent of .alpha.,.omega.-dihalogeno-alkane and simultaneously the electrochemical reduction of a compound of titanium (IV) occur in process.The catalytic composition comprises at least one titanium compound, at least one halogenated organo-aluminum compound and at least one inorganic magnesium compound in suspension in at least one .alpha.,.omega.-dihalogeno-alkane. The titanium compound is essentially a titanium (III) compound. The overall content of titanium (II) and titanium (IV) is less than or equal to 15% of the total titanium content.