Abstract: The present invention pertains to a process for preparing a rubber precursor or a rubber composition comprising a modified inorganic oxygen-containing particulate material comprising the steps of: a) preparing a mixture of the modified inorganic oxygen-containing particulate material and a first solvent; and b1) adding the mixture to a rubber precursor comprising at least one polymer and optionally a second solvent; or b2) adding the mixture to a rubber composition comprising at least one monomer of a rubber precursor and optionally a second solvent, and polymerising the monomer(s) to form the rubber precursor; c) optionally cross-linking the rubber precursor in the presence of a cross-linking agent to form a rubber composition; and d) optionally removing the first and/or second solvents before, during or after any of the steps b1), b2), and c). The invention further pertains to rubber compositions comprising rubber and inorganic oxygen-containing particulate material modified with a coupling agent.