A process for the preparation of a solid catalyst component for the polymerization of CH2═CHR olefins, wherein R is hydrogen or hydrocarbyl radical with 1-12 carbon atoms, made from or containing a Ti compound on a Mg chloride based support, including the steps of (a) reacting a Mg based compound with a liquid medium made from or containing a Ti compound, at a temperature ranging from 0 to 150° C., thereby yielding solid particles; and (b) suspending the solid particles coming from step (a) in a liquid medium made from or containing hydrocarbons at a temperature ranging from 10 to 100° C., wherein step (a) or (b) is carried out in the presence of 0.2 to 20.0% by weight, with respect to the amount of Mg compound, of particles of a solid compound containing more than 50% by weight of SiO2 units and having average particle size from 1 to 100 μm.