The present invention relates to a process for preparing a catalyst solid for olefin polymerization, comprising a finely divided support, an aluminoxane and a metallocene compound, which comprises a) firstly combining the finely divided support with the aluminoxane and subsequently b) adding the reaction product of a metallocene compound with at least one organometallic compound to the modified support, catalyst solids obtainable by this process, catalyst systems comprising these catalyst solids, their use for the polymerization of olefins and a process for the polymerization of olefins.