The present invention relates to an improved CuAl2O4 spinel based catalyst additive composition having bi-modal pore size for improving gasoline sulfur removal activity by maintaining high gasoline selectivity and maintaining research octane number (RON) while cracking heavier hydrocarbon feedstocks in the fluid catalytic cracking unit. More particularly, present invention relates to a gasoline sulfur reduction (GSR) additive comprising copper aluminate spinel, acidic alumina matrix; and clay, wherein the additive having bimodal pore distribution. Present invention also relates to a process for preparing the gasoline sulfur reduction (GSR) additive.