The invention is directed to a process for producing a particulate support for an olefin polymerisation catalyst wherein a solution of a magnesium compound is contacted with a solution of an element of Group (13 or 14) of the Periodic Table (IUPAC) to obtain a solid reaction product. In the process of the invention the solid reaction product is formed by: i) contacting (a) a solution of a magnesium hydrocarbyloxy compound with (b) a solution of a halogen-containing compound of an element of Group (13 or 14) of the Periodic Table (IUPAC); and ii) recovering the solidified reaction product from the reaction mixture.