A magnesium halide adduct is provided, comprising at least one compound of the formula MgXY, at least one compound of the formula ROH, methanol, at least one modifying agent chosen from DOE and o-hydroxy benzoates, and optionally water. Also provided herein are a catalyst component comprising the magnesium halide adduct, a catalyst for olefin polymerization comprising the catalyst component; the respective processes for preparing the magnesium halide adduct and the catalyst component; use of the magnesium halide adduct for preparing the catalyst component, use of the catalyst component in a catalyst for olefin polymerization and use of the catalyst in olefin polymerization; and a process of olefin polymerization.