To develop a novel additive that has excellent olefin reduction capability for FCC gasoline without loss in octane number, different additives based on magnesia-alumina spinel were prepared by sol-gel method. The catalytic activities of additives for reducing the olefins in the fluid catalytic cracking (FCC) gasoline were assessed in a micro fixed bed reactor and the influences of Mg/Al ratio, the modification of La and Nb on the additive performance were studied as well. Results indicated that the additive with the Mg/Al ratio of 1.0 possessed the highest reaction activity due to the formation of MgAl2O4 center dot MgO spinel. The activities of additives modified by La and Nb were also improved, for example, the reaction activity of additive with 4-5 wt% La was 34%. The XRD results showed that the effect of reducing olefin was the function of both MgAl2O4 center dot MgO spinel and LamOn or MgAl2O4 center dot MgO spinel and Nb2O5.